Enhancing Mechanistic Research on Precision Probiotic Therapies (R33 Clinical Trial Optional) | PAR 25 210

Opportunity Information: Apply for PAR 25 210

The NIH funding opportunity "Enhancing Mechanistic Research on Precision Probiotic Therapies (R33 Clinical Trial Optional)" (PAR-25-210) is designed to push probiotic research beyond one-size-fits-all approaches by funding mechanistic studies that explain why probiotics help some people but not others. The central focus is precision probiotic therapy: figuring out which person-specific characteristics shape probiotic response, using that knowledge to identify distinct responder subgroups, and then using mechanistic insight to improve clinical outcomes. Rather than simply testing whether a probiotic works on average, this program is aimed at uncovering the biological reasons behind inconsistent results in human studies and translating those insights into strategies that make probiotic interventions more reliable.

A key emphasis of the NOFO is heterogeneity in human hosts and how that heterogeneity creates variable probiotic effects. Applicants are expected to investigate "host biological patterns" that correlate with probiotic use and outcomes, such as the native microbiome composition and function, immune status, sex or gender-related biology, diet, age, genetic background, lifestyle factors, and relevant health history. The intent is to evaluate whether these patterns can be used to detect, predict, or explain improvements in probiotic responsiveness. In practical terms, projects should aim to link measurable host features to differences in colonization, persistence, metabolic activity, immune modulation, or other mechanistic pathways that could explain why the same probiotic strain performs differently across individuals.

This is an R33 mechanism, meaning the work is expected to be more advanced and positioned for well-defined mechanistic testing. The NOFO is particularly well matched to projects where investigators already have supportive preliminary data indicating specific host features that may be driving probiotic response, but where additional studies are needed to test causality, clarify mechanisms, or establish predictive value. The program is not primarily meant for exploratory discovery of new host-response patterns from scratch; investigators who are still in the early stage of identifying candidate host patterns are directed toward a companion R61/R33 opportunity (PAR-AT-24-XXX, TEMP-25412), which is structured to support earlier development and validation steps before the later-stage mechanistic push.

Methodologically, the NOFO calls for rigorously designed mechanistic research conducted either in humans or in relevant and innovative animal models. The emphasis on "mechanistic" signals that proposals should go beyond descriptive correlations and instead test how and why a given host factor changes probiotic function or host response. Depending on the project, that might include experimentally manipulating diet, immune pathways, or microbial community structure; testing defined strains or consortia under controlled conditions; using translational model systems that capture human-like variation; and applying robust analytical frameworks that can distinguish association from causal influence. The "Clinical Trial Optional" designation indicates that clinical trials are allowed but not required; applicants can propose human interventional studies when appropriate, or remain in preclinical/translational mechanistic work, as long as the research directly advances precision understanding of probiotic responsiveness.

Eligibility is broad and includes many types of domestic organizations and government entities, such as state, county, and local governments; public and private institutions of higher education; independent school districts; special district governments; federally recognized tribal governments and other tribal organizations; public housing authorities/Indian housing authorities; nonprofits (with or without 501(c)(3) status); for-profit organizations (other than small businesses) and small businesses; and other eligible applicants. The NOFO also highlights inclusion of organizations such as HBCUs, Hispanic-serving institutions, AANAPISIs, Alaska Native and Native Hawaiian Serving Institutions, Tribally Controlled Colleges and Universities, faith-based and community-based organizations, regional organizations, eligible federal agencies, and U.S. territories or possessions. Foreign organizations are not eligible to apply, and non-U.S. components of U.S. organizations are not eligible to apply; however, foreign components (as NIH defines them in the NIH Grants Policy Statement) may be included when justified, which allows certain international elements to contribute to the science without a foreign organization serving as the applicant.

From an administrative standpoint, this is a discretionary NIH grant opportunity (CFDA/Assistance Listing numbers include 93.121, 93.213, 93.313, 93.393, and 93.866). The posted original closing date is 2027-06-02. The announcement does not specify an award ceiling or the expected number of awards in the provided summary fields, so applicants would typically confirm budget and award expectations by reviewing the full NOFO text and any NIH institute-specific guidance tied to this program.

Overall, the opportunity is best understood as a targeted investment in precision medicine for probiotics: supporting studies that can stratify patients or consumers into meaningful biological subgroups, explain mechanistically why those groups respond differently, and develop practical strategies to overcome barriers that currently make probiotic effects inconsistent across diverse human populations.

• The National Institutes of Health in the education, health sector is offering a public funding opportunity titled "Enhancing Mechanistic Research on Precision Probiotic Therapies (R33 Clinical Trial Optional)" and is now available to receive applicants.
• Interested and eligible applicants and submit their applications by referencing the CFDA number(s): 93.121, 93.213, 93.313, 93.393, 93.866.
• This funding opportunity was created on 2024-10-31.
• Applicants must submit their applications by 2027-06-02.
• Eligible applicants include: State governments, County governments, City or township governments, Special district governments, Independent school districts, Public and State controlled institutions of higher education, Native American tribal governments (Federally recognized), Public housing authorities/Indian housing authorities, Native American tribal organizations (other than Federally recognized tribal governments), Nonprofits having a 501 (c) (3) status with the IRS, other than institutions of higher education, Nonprofits that do not have a 501 (c) (3) status with the IRS, other than institutions of higher education, Private institutions of higher education, For-profit organizations other than small businesses, Small businesses, Others.

Apply for PAR 25 210

[Watch] Creating a grant proposal using the step-by-step wizard inside the applicant portal: