Can gut bacteria make CAR-T therapy safer and stronger?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Patients with a histologically confirmed Large B-Cell Lymphoma (LBCL) or Multiple Myeloma (MM) who are to receive a commercial Chimeric Antigen Receptor T-Cell (CAR-T) product per individual investigator. * Age ≥18 years. * ECOG performance status ≤2 (Karnofsky ≥60%). * Patient meets the eligibility criteria for the commercial CAR-T product they will receive (axi-cel, liso-cel, or cilta-cel), including the organ function, hematologic, and cardiopulmonary thresholds specified by institutional standard-of-care eligibility for CAR-T administration. * Ability to understand and the willingness to sign a written informed consent document. Exclusion Criteria: * Patients who are receiving any other investigational agents. * Inability to swallow capsules. * Patients with known intestinal barrier dysfunction, including clinically active IBD (Crohn's or ulcerative colitis), GI bleed, enteropathy (including celiac disease), ischemic colitis, microscopic colitis, graft versus host disease, or malignant involvement of GI tract. * History of behavioral disorders, including substance abuse disorders, which, in the discretion of the primary investigator, will interfere with safe conduct and compliance with study treatment. * Diagnosis of primary immunodeficiency. * Active second malignancy requiring treatment except non-melanoma skin cancer or carcinoma in situ of the cervix, bladder, or non-metastatic prostate cancer which does not require treatment. * Active treatment (within 24 hours of LBP administration) for a bacterial, fungal, or viral infection confirmed using clinical, laboratory, and radiographic findings. Prophylactic antivirals, anti-fungals, and anti-bacterial (levofloxacin, cefdinir, and trimethoprim-sulfamethoxazole) are allowed. * Any clinical, laboratory, or radiologic findings, at the discretion of the primary investigator, will interfere with the safe conduct of study treatment and compliance with study procedures. * Documented severe hypersensitivity reaction (e.g., anaphylaxis, angioedema, Stevens-Johnson syndrome, toxic epidermal necrolysis, or DRESS) precluding safe administration of all four of the following antibiotics: ampicillin/sulbactam, piperacillin/tazobactam, metronidazole, and meropenem. These four agents have confirmed in vitro activity against every strain in the consortium; concurrent contraindication to all four would preclude empiric antibiotic coverage in the unlikely event of bacteremia from a consortium organism. Self-reported drug intolerance (e.g., nausea, headache, non-specific rash without systemic features) does not meet this criterion; ambiguous allergy histories should be reviewed with the Sponsor-Investigator and, when feasible, evaluated by an allergist for de-labeling prior to exclusion. * History of allergic reactions attributed to any of the investigational products or components. * Ileostomy, colostomy, or resection of over 50% of the large bowel. * Pregnant or breastfeeding women.