A Bifidobacterium bifidum strain and its application in adjuvant therapy of tumors

Abstract

The present invention discloses a Bifidobacterium bifidum strain and its application in adjuvant tumor therapy. The strain is named B.bifidum Zhang2021, which was deposited in the China Center for Type Culture Collection on September 5, 2022, with a deposit number of CCTCC M 20221374. It is identified as a newly discovered Bifidobacterium bifidum strain, and animal experiments have confirmed that the Bifidobacterium bifidum strain can effectively enhance the therapeutic effect of the immune checkpoint inhibitor PD-1 monoclonal antibody. The newly discovered Bifidobacterium bifidum strain in the present invention can be used to prepare biological preparations or drugs for human immunoregulation or tumor immunoadjuvant therapy, with diverse dosage forms and no toxic side effects, and has good application prospects.

Description

Technical Field

[0001] The invention belongs to the field of biomedicine, and specifically relates to a Bifidobacterium bifidum strain and an application thereof in adjuvant tumor treatment. Background Art

[0002] Cancer is one of the most serious diseases threatening human life and health, and its morbidity and mortality are on the rise worldwide. At present, surgery, radiotherapy, chemotherapy and biological therapy have made significant progress, but the mortality rate of advanced malignant tumors is still very high. In recent years, immunotherapy has developed rapidly. The body's own immune system not only has the function of immune surveillance, but also can promote tumor immune escape at certain stages, playing an important role in the occurrence and development of tumors. Inhibitors targeting immune checkpoints (ICI) are a new type of immunotherapy drugs. Among them, monoclonal antibodies targeting programmed cell death protein-1 (PD-1 monoclonal antibodies) have achieved good results in the treatment of various advanced tumors. Since its advent, ICI has been used to treat a variety of tumors and has achieved good therapeutic effects in 20%-30% of patients. However, most tumor patients still have an extremely low initial treatment response rate to ICI, or they quickly develop secondary resistance, which greatly limits the clinical application and promotion of ICI. Therefore, overcoming ICI resistance and improving the response rate of ICI treatment have become hot and difficult issues in the field of tumor treatment.

[0003] The intestinal flora is a complex microbial community composed of more than 1,000 species of bacteria living in the human intestine. The intestinal flora participates in many basic physiological activities of the human body, such as promoting intestinal maturation, digestion and absorption of food, synthesizing vitamins, resisting the invasion of pathogens, maintaining the intestinal barrier, and maintaining the homeostasis of the immune system. Recent studies have shown that the intestinal flora can affect the immunotherapy effect of patients with melanoma, non-small cell lung cancer, and renal cancer, which provides a new idea for improving the efficacy of PD-1 monoclonal antibodies in the treatment of malignant tumors. The study found that in 249 tumor patients treated with PD-1 monoclonal antibodies, the therapeutic effect of PD-1 monoclonal antibodies was significantly reduced when antibiotics were used to remove their own intestinal flora. Microbial analysis found that Akkermansiamuciniphila was significantly enriched. After being gavaged to mice with poor response to PD-1 monoclonal antibodies, it can produce a good response, and the effector lymphocytes in its tumor microenvironment increased significantly. Similarly, the University of Chicago in the United States also found that in patients with metastatic melanoma, the intestinal symbiotic microbiome of patients was associated with the efficacy of PD-1 monoclonal antibodies. All of the above indicate that the intestinal flora affects the therapeutic effect of PD-1 monoclonal antibodies, suggesting that the anti-tumor effect of PD-1 monoclonal antibodies can be improved by adjusting the intestinal flora, including oral probiotics and fecal microbiota transplantation to regulate the intestinal flora.

[0004] Although current preclinical animal experiments and small-sample clinical studies have found that certain intestinal flora can affect the therapeutic effect of ICI, the mechanism by which intestinal flora affects the therapeutic effect of ICI is still not very clear. In addition, the effects of intestinal flora from different donors on the efficacy of ICI are different, and the effects of the same donor's flora transplanted to different recipients on the therapeutic effect of ICI are also different. At the same time, intestinal bacteria isolated by scientists from France, the United States, and Japan that affect the therapeutic effect of ICI also show racial differences. All of the above have prompted researchers to further explore better and more spectrally effective bacterial species in the intestinal flora to improve the therapeutic effect of ICI, and explore their mechanisms of action to promote better clinical application of ICI drugs. Previous studies have found that dietary fiber pectin can significantly improve the intestinal flora of tumor-bearing mice, and Bifidobacterium enriched with dietary fiber pectin has a significant promoting effect on the therapeutic effect of PD-1 monoclonal antibody (Theranostics. 2021Feb 19; 11(9): 4155-4170.), which suggests that Bifidobacterium microorganisms may be the main participants in regulating tumor immune responses. Based on this, Bifidobacterium strains were targeted for isolation, culture and identification, and their effects on ICI treatment of malignant tumors were tested, thereby completing the present invention. Summary of the invention

[0005] The present invention provides a Bifidobacterium bifidum strain, which is named B.bifidumZhang2021 and is preserved in the China Type Culture Collection (CCTCC) located at 299 Bayi Road, Wuchang District, Wuhan City, Hubei Province, on the campus of Wuhan University, with a preservation date of September 5, 2022 and a preservation number of CCTCC M 20221374.

[0006] Preferably, the Bifidobacterium bifidum strain is derived from human excreta.

[0007] The aforementioned Bifidobacterium bifidum strain of the present invention is obtained by the following isolation, culture and identification methods:

[0008] (1) Strain isolation

[0009] 1a) fresh feces from healthy volunteers who had long-term dietary fiber pectin were collected, weighed under anaerobic sterile conditions, diluted with Wilkins-Chalgren anaerobic broth at a mass ratio of 1:9, and vibrated to obtain a fecal suspension;

[0010] 1b) Use an inoculation loop to pick up the above suspension and streak it on an MRS agar plate. The streaked plate is placed in a constant temperature anaerobic culture at 37°C for 72 hours;

[0011] 1c) Select a single bacterial plaque, inoculate it in a Bifidobacterium selective liquid culture medium, and culture it anaerobically at 37°C for 48 hours. Observe the colony morphology and perform Gram staining. Code the Gram-positive colonies and further purify and culture them.

[0012] (2) Strain identification

[0013] 2a) centrifuging and concentrating the isolated and purified Bifidobacterium bacteria, and testing and confirming that the isolated bacteria are Bifidobacterium bacteria;

[0014] 2b) Expansion culture of Bifidobacterium bacteria;

[0015] 2c) extracting DNA from the centrifuged and concentrated bacteria, amplifying the 16S rDNA V3-V4 region sequence, and sequencing the amplified product, which showed that the isolated bacteria were Bifidobacterium;

[0016] 2d) The bacterial whole genome De Novo third-generation sequencing technology was used to obtain the complete genome map information of the B. bifidum isolated this time, and the ANI index was calculated, suggesting that it was a newly discovered strain, named B. bifidum Zhang2021, and preserved in the China Center for Type Culture Collection, No. 299, Bayi Road, Wuchang District, Wuhan City, Hubei Province. The preservation date is September 5, 2022, and the preservation number is CCTCC M 20221374.

[0017] The present invention also provides the use of the Bifidobacterium bifidum strain in preparing a biological preparation for human immune regulation or tumor immune-assisted treatment.

[0018] The present invention also provides a biological preparation, which comprises the aforementioned Bifidobacterium bifidum strain of the present invention as an active ingredient.

[0019] Preferably, the biological preparation further comprises a pharmaceutically acceptable carrier or excipient, and the dosage form comprises tablets, capsules, granules, pills, powders, granules, pastes, suspensions, oral solutions or injections.

[0020] Preferably, the number of viable bacteria of the Bifidobacterium bifidum strain is not less than 1×10 6 CFU / mL or 1×10 6CFU / g.

[0021] The present invention also provides the use of the Bifidobacterium bifidum strain in the preparation of a biological preparation or a drug for enhancing the effect of an immune checkpoint inhibitor in treating tumors.

[0022] Preferably, the immune checkpoint inhibitor is PD-1 monoclonal antibody.

[0023] Preferably, the Bifidobacterium bifidum strain is used in combination with the PD-1 monoclonal antibody.

[0024] Preferably, the tumor is colorectal cancer.

[0025] The present invention also provides the use of the Bifidobacterium bifidum strain in the preparation of medicines for improving intestinal flora microecology or preventing and treating immune-related colitis.

[0026] Compared with the prior art, the present invention obtains a newly isolated Bifidobacterium bifidum strain by targeted separation and cultivation of strains derived from humans. It is identified that it is completely different from known strains with immunomodulatory effects such as Akkermansia muciniphila, Bifidobacterium pseudolongum, Lactobacillus johnsonii and other intestinal bacteria, and can effectively enhance the therapeutic effect of immune checkpoint inhibitors. At the same time, animal experiments have confirmed that the Bifidobacterium bifidum strain can effectively enhance the therapeutic effect of the immune checkpoint inhibitor PD-1 monoclonal antibody, and it can synergize with the PD-1 monoclonal antibody to improve the tumor immune microenvironment, enhance the body's anti-tumor immune response, and significantly inhibit the growth rate of colorectal tumors. It shows that the newly isolated Bifidobacterium bifidum strain obtained by the present invention can be used to prepare biological preparations or drugs that enhance the therapeutic effect of immune checkpoint inhibitors, and the dosage form administration form is diverse and has no toxic side effects, providing an auxiliary treatment method for tumor immunotherapy, and has a good application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is the isolation, cultivation and identification of B.bifidum Zhang2021 in the embodiment, wherein: A) 16S rDNA sequencing technology is used to perform first-generation sequencing on the isolated strain; B) the whole genome of B.bifidum is sequenced, and the assembled genome is compared and analyzed with the known B.bifidum in the NCBI data.

[0028] Figure 2This is a colony characteristic diagram of B. bifidum Zhang2021 in the example.

[0029] Figure 3 The present invention shows that B.bifidum Zhang2021 improves the therapeutic effect of tumor models with ICI treatment resistance, wherein: A) tumor growth curves in the control group, PD-1 monoclonal antibody group, B.bifidum Zhang2021 group, and PD-1 monoclonal antibody + B.bifidumZhang2021 group; B) tumor mass of tumor-bearing mice in each group at the end of the experiment; C) weight changes of tumor-bearing mice in each group during the experiment.

[0030] Figure 4 This is the result of HE staining analysis of the safety of B. bifidum Zhang2021 on the main organs (heart, liver, lung, and kidney) of tumor-bearing mice in the example.

[0031] Figure 5 In the embodiment, flow cytometry analysis of B. bifidum Zhang2021 was used to increase CD8 + T cell infiltration, thereby promoting the therapeutic effect of anti-tumor immune response in tumor-bearing mice.

[0032] Figure 6 These are the test results of using B. bifidum Zhang2021 in the example to improve the richness and diversity of intestinal flora in mice with colorectal cancer, wherein: A) β-diversity analysis of fecal samples based on Bray-Curtis distance; B-C) ​​Observed species (B) and (C) to evaluate the α diversity of intestinal flora between groups; D) the composition ratio of intestinal flora in each group of mice with colorectal cancer at the family level.

[0033] Figure 7 This is a heat map of the effects of B. bifidum Zhang2021 on intestinal microorganisms at the genus level in the Example.

[0034] Figure 8 This is the HE staining result of the colon tissue of the colorectal cancer mice in the Example. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0036] Example 1

[0037] This example is to isolate, culture and identify the strain of Bifidobacterium bifidum, as follows: collect the first fresh feces discharged in the morning from a healthy volunteer (male, 31 years old, without gastrointestinal infectious diseases, and without taking antibiotics, probiotics and prebiotics within 3 months) who has been consuming dietary fiber pectin for a long time, weigh the mass under anaerobic sterile conditions, add Wilkins-Chalgren anaerobic broth to dilute at a mass ratio of 1:9, and obtain a fecal suspension after oscillation and mixing. Dilute with 0.9% saline (volume ratio 1:100); dip the above dilution with a bacterial loop, streak on the prepared MRS agar plate, and place the streaked plate at 37°C for constant temperature anaerobic culture for 72h; select a single plaque, inoculate it in a Bifidobacterium bacteria selective liquid culture medium, and culture it at 37°C for 48h, and concentrate the bacteria by centrifugation.

[0038] According to the conservation of the two ends of the 16S rDNA sequence of different species of bacteria, universal primers were designed to amplify the 16SrDNA V3-V4 region sequence of the strain by PCR, and the amplified target fragment was sequenced by first generation sequencing. The sequencing results showed that the isolated bacteria were Bifidobacterium bifidum (abbreviated as B.bifidum) ( Figure 1 A). The whole genome of the B. bifidum strain was further sequenced by De Novo sequencing. The assembled genome was compared with the strain sequence of B. bifidum in the NCBI data, the whole genome map of the B. bifidum strain was constructed, and the ANI index was calculated. The results suggested that it was a newly discovered strain, and the strain was named B. bifidum Zhang2021( Figure 1 B), has been deposited in the China Center for Type Culture Collection, the deposit number is CCTCC M 20221374, the deposit date is September 5, 2022, and the deposit address is No. 299, Bayi Road, Wuchang District, Wuhan City, Hubei Province.

[0039] Example 2

[0040] In this example, the living bacterial liquid of B. bifidum Zhang2021 was prepared in the following steps:

[0041] 1) Inoculate B. bifidum Zhang2021 strains on blood plates and culture them anaerobically for 48 hours. Observe the colony morphology, staining characteristics, size, club shape and distribution.

[0042] Colony characteristics: After culturing on a blood plate at 37°C for 48 hours, B.bifidum Zhang2021 is rod-shaped or forked, slightly white, opaque, with a smooth to mucous soft surface, no mycelium, and a colony diameter between 1-3 mm ( Figure 2 ).

[0043] 2) B.bifidum Zhang2021 strain expansion: Select a single colony from step 1) and inoculate it into modified MRS medium (basic ingredients: tryptic peptone: 5.0 g / L; soy peptone: 5.0 g / L; yeast extract powder: 10.0 g / L; glucose: 10.0 g / L; L-cysteine: 0.5 g / L; resazurin: 0.001 g / L; potassium dihydrogen phosphate: 0.04 g / L; potassium hydrogen phosphate: 0.04 g / L; sodium bicarbonate: 0.4 g / L; sodium chloride: 0.08 g / L; calcium chloride: 0.008 g / L; magnesium sulfate heptahydrate: 0.22 g / L; magnesium sulfate monohydrate: 0.05 g / L; Tween 80: 1.0 g / L) for bacterial enrichment culture, and the obtained bacterial solution is stored for later use.

[0044] 3) B. bifidum Zhang2021 live bacterial solution: The bacterial solution prepared in step 1) was measured for OD 600nm and viable bacterial count, and diluted to 10 with physiological saline. 7 CFU / mL and 10 9 CFU / mL, save for future use.

[0045] Example 3

[0046] The preparation method of B.bifidum Zhang2021 powder is as follows: continue to expand the culture with the isolated B.bifidum Zhang2021 strain; after culturing to the logarithmic phase, centrifuge to obtain B.bifidum Zhang2021 precipitate; resuspend 10g B.bifidum Zhang2021 precipitate with 1000mL 0.9% physiological saline, centrifuge the suspension again, and collect the precipitate; resuspend 10g B.bifidum Zhang2021 precipitate with 100mL 0.9% physiological saline again, centrifuge the suspension again, collect the precipitate to obtain B.bifidum Zhang2021 bacterial mud, and vacuum freeze-dry the bacterial mud to obtain B.bifidum Zhang2021 bacterial powder.

[0047] B.bifidum Zhang2021 biological preparations can be tablets, capsules, granules, pills, powders, granules, pastes, suspensions, oral solutions or injections, etc. Taking capsules as an example, the preparation method is as follows: first take 1g of B.bifidumZhang2021 powder, then add 0.1g of dietary fiber oligopectin, and finally put it into hydroxypropylmethylcellulose capsules to obtain B.bifidum Zhang2021 capsules (the total number of live bacteria in 1g of finished product is equivalent to 45 billion / gram).

[0048] Example 4

[0049] In this example, 6-8 week old C57BL / 6 female mice and colorectal cancer cell line MC38 were used to construct a tumor-bearing mouse model with ICI treatment resistance, and the effect of B. bifidum Zhang2021 on a tumor model with ICI treatment resistance was tested, wherein the immune checkpoint inhibitor was PD-1 monoclonal antibody (InVivoMAb anti-mouse PD-1, Bio X cell Co. Ltd. USA, #BE0146).

[0050] MC38 cells in the logarithmic growth phase were taken and made into a single cell suspension of 2.0×10 6 0.2 mL of cell suspension (5.0×10 5 The model was successfully established when a small tumor mass grew at the inoculation site of the mouse. The mice were raised in an SPF-grade animal room with a breeding environment of 20-23°C, 40%-70% humidity, 12h light and 12h dark. The feed and bedding were sterilized by 60Co-γ and 50kGy radiation, and the drinking water, mouse cages and drinking bottles were sterilized by high temperature and high pressure before use. The tumor volume reached 100mm 3 At 4 d0, the mice were randomly divided into 4 groups, namely, control group, B.bifidum Zhang2021 group, PD-1 antibody group, and PD-1 monoclonal antibody + B.bifidum Zhang2021 group, with 6-8 mice in each group.

[0051] Starting from D0, the animals in the control group and B. bifidum Zhang2021 group were orally administered with 300 μL of normal saline daily and intraperitoneally injected with 200 μL of PBS twice a week. Each drug group was given the corresponding drug at the same frequency. The volume of B. bifidum Zhang2021 bacterial solution was 300 μL (bacterial number: 1.0×10 9CFU / mouse), the PD-1 antibody administration volume was 200μL (dosage: 200ug / mouse). After tumor formation, the health status and death of the animals were observed every day, and the tumor diameter (long diameter and short diameter) was measured every three days. The mouse tumor volume calculation formula was: V = 0.5 × long diameter × short diameter × short diameter. On the 30th day, all mice were euthanized, and the hearts, livers, lungs, kidneys, colons and tumor tissues of the mice were collected and repeatedly rinsed with pre-cooled PBS. The tumor tissue was weighed and measured, and photographed and recorded. The removed tissue was divided into two, one was placed in formalin solution; the other was quick-frozen in liquid nitrogen, and then stored in a -80°C refrigerator.

[0052] like Figure 3 As shown in A, PD-1 monoclonal antibody has a weak inhibitory effect on tumor growth, while the anti-tumor ability of B.bifidum Zhang2021 even exceeds that of PD-1 monoclonal antibody. The combined use of PD-1 monoclonal antibody + B.bifidum Zhang2021 can significantly inhibit tumor growth, and the therapeutic effect is significantly better than the use of PD-1 monoclonal antibody or B.bifidum Zhang2021 alone. At the end of the experiment, the tumor mass of each group of mice also confirmed this result ( Figure 3 B). In addition, the weight of mice in each group maintained a steady increase throughout the experiment, and there was no significant difference in weight between the groups ( Figure 3 C). In summary, B. bifidum Zhang2021 can improve the therapeutic effect of PD-1 monoclonal antibody on ICI-resistant colorectal cancer without significant effect on body weight.

[0053] Example 5

[0054] This example verifies the safety of B. bifidum Zhang2021 combined with PD-1 monoclonal antibody in tumor-bearing mice. HE staining analysis was performed on the main organs of the mice, including the heart, liver, lungs, and kidneys, and it was found that no morphological and pathological damage was found in each organ ( Figure 4 ), suggesting that the combined use of B. bifidum Zhang2021 and PD-1 monoclonal antibody has no obvious adverse effects on normal tissues and has a high safety profile.

[0055] Example 6

[0056] Tumor infiltrating lymphocytes (TILs) are a type of atypical lymphocytes, mainly T cells, that exist in tumor nests and stroma, and have tumor infiltration and antigenic effects. Studies have found that in many solid tumors such as melanoma and ovarian cancer, the degree of TILs infiltration in the tumor microenvironment is often closely related to prognosis. Recent studies have divided solid tumors into two types: "hot" tumors and "cold" tumors. "Cold" tumors have less TILs infiltration and usually respond poorly to monotherapy with PD-1 monoclonal antibodies. This is also the main obstacle to the effective treatment of PD-1 monoclonal antibodies in tumor patients. Researchers around the world are trying to develop strategies to transform "cold" tumors into "hot" tumors. Currently, improving the infiltration level of TILs by regulating the intestinal flora is a hot research field, but it is still in the early stages of exploration.

[0057] In this example, flow cytometry was used to detect the infiltration level of TILs in the tumor tissues of the control group and the B.bifidum Zhang2021+PD-1 monoclonal antibody group, thereby verifying that B.bifidum Zhang2021 increased the infiltration of TILs cells in the tumor microenvironment and promoted the therapeutic effect of PD-1 monoclonal antibody. Figure 5 As shown in the figure, compared with the control group, the B.bifidum Zhang2021 group or the B.bifidum Zhang2021+PD-1 monoclonal antibody group upregulated the CD4 + T and CD8 + The proportion of T cells in total cells, and these two cells play a key role in the body's anti-tumor immune response. Moreover, the upregulation in the B.bifidumZhang2021+PD-1 antibody group was greater than that in the single-dose group. The results showed that B.bifidum Zhang2021 can increase the infiltration of TILs cells in the tumor immune microenvironment, promote the formation of a "hot" tumor microenvironment, and thus enhance the anti-tumor effect of PD-1 monoclonal antibodies. The above results suggest that the increase in TILs infiltration induced by B.bifidum Zhang2021 is one of the promising strategies to transform "cold" tumors into "hot" tumors, which can be used in tumor treatment or as an immunomodulator to enhance the immunotherapy effect of PD-1 monoclonal antibodies.

[0058] Example 7

[0059] This example verifies the effect of B. bifidum Zhang2021 on the intestinal flora of mice with colorectal cancer. The feces of mice in each group were collected on the 27th day after tumor inoculation, and the bacterial 16S rDNA (V3-V4 region) in the feces was sequenced and analyzed by Illumina MiSeq. First, the Bray-Curtis dissimilarity coefficient between the genus-level difference matrices was calculated to reflect the β diversity of its species ( Figure 6A), the results suggest that B.bifidum Zhang2021 intervention can increase the degree of difference between microbial communities. At the same time, B.bifidum Zhang2021 intervention increased the α diversity of intestinal microorganisms, including Observed species ( Figure 6 B) and Shannon index ( Figure 6 C), B. bifidum Zhang2021 intervention can improve the microbial species at the family level ( Figure 6 D), these results indicate that B.bifidum Zhang2021 treatment significantly increased the richness and diversity of intestinal flora. In addition, the specific changes in intestinal flora in each group were analyzed at the genus level in the experiment. The genus level community analysis showed that mice treated with B.bifidumZhang2021 showed a trend towards a robust intestinal microecological evolution. For example, beneficial bacteria that play a key role in maintaining intestinal homeostasis, such as Lactobacillus, Faecalibaculum, Ruminiclostridium, Akkermansia and Ruminococcus, increased significantly after B.bifidum Zhang2021 intervention. At the same time, B.bifidum Zhang2021 can significantly inhibit the growth of harmful bacteria such as Acinetobacter, Streptococcus and Acetatifactor ( Figure 7 ).

[0060] A healthy intestinal microenvironment is the basis for the existence of a normal intestinal barrier. However, PD-1 monoclonal antibodies can cause some immune-related adverse reactions, especially in patients with intestinal dysbiosis. One of the most common toxicities is immune-related colitis. To this end, pathological analysis of the colon tissues of each group of mice was performed, and it was found that compared with the PD-1 monoclonal antibody group, after oral administration of B. bifidum Zhang2021 strain, the infiltration of inflammatory cells was reduced, the glandular structure was restored, and the colon tissue structure was relatively intact ( Figure 8 ), suggesting that oral administration of B.bifidum Zhang2021 may maintain the homeostasis of the intestinal environment by regulating the intestinal flora, thereby providing a complete intestinal barrier to inhibit the occurrence of diarrhea and colitis associated with immune checkpoint inhibitors. In summary, compared with the control group, B.bifidum Zhang2021 can effectively increase the richness and diversity of the intestinal flora of colorectal cancer mice, promote the formation of a robust intestinal microecology in mice, and reduce the occurrence of immune-related colitis.

[0061] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A Bifidobacterium bifidum strain, named B. bifidum Zhang2021, deposited in the China Type Culture Collection, Wuhan University, No. 299, Bayi Road, Wuchang District, Wuhan City, Hubei Province, with a deposit date of September 5, 2022 and a deposit number of CCTCC M 20221374; The Bifidobacterium bifidum strain is derived from human excreta.

2. A medicine comprising the Bifidobacterium bifidum strain according to claim 1 as an active ingredient; The drug also includes a pharmaceutically acceptable carrier, and the dosage form includes tablets, capsules, granules, pills, powders, granules, pastes, suspensions, oral solutions or injections; The number of viable bacteria of the Bifidobacterium bifidum strain is not less than 1×10 6 CFU / mL or 1×10 6 CFU / g.

3. Use of the Bifidobacterium bifidum strain according to claim 1 in the preparation of a drug for enhancing the effect of immune checkpoint inhibitors in treating tumors; The immune checkpoint inhibitor is a PD-1 monoclonal antibody; The Bifidobacterium bifidum strain is used in combination with PD-1 monoclonal antibody; The tumor is colorectal cancer.

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