Supplementation with heat-sterilized Lactobacillus crispatus strain KT-11 stimulates the T cell-related immune function of healthy Japanese adults: A pilot randomized, placebo-controlled, double-blind, parallel-group study.

Viral infections are a global public health threat, reaffirming the importance of immune function. We previously identified Lactobacillus crispatus strain KT-11 (KT-11) and found that heat-sterilized KT-11 affect counts of T cell and dendritic cell in vitro, as well as promoted immunoglobulin A production and prevented weight loss caused by influenza virus infection in vivo. It was hypothesized that heat-sterilized KT-11 affects immune cell count/activity even in healthy individuals. We conducted a pilot study to examine the design to verify the effects of heat-sterilized KT-11 supplementation on immune cell count/activity and physical condition. This was a pilot randomized, double-blind, placebo-controlled, parallel-group study including 22 healthy adults who consumed either KT-11 or placebo for 4 weeks. Immunological status (immune cell count/activity and its score) and various immune-related indicators including SARS-CoV-2 immunoglobulin G antibody were assessed, and a physical condition questionnaire was administered. The primary outcome was immune cell count/activity (T cell subsets, B cell, natural killer cell) and overall immunological status score after 4 weeks. Two patients were excluded because of noncompliance; the final analysis included 20 participants (10 participants/group). The KT-11 group had a significantly higher CD3+ T cell count versus placebo group. The female subgroup also had a significantly higher CD8+CD28+ T cell count. Although the KT-11 group showed no changes in SARS-CoV-2 immunoglobulin G titer, it had fewer self-reported common cold-like symptoms, particularly fatigue. This pilot study showed that KT-11 affected immune cell profiles, suggesting that the feasibility of a verification study. This trial was registered at UMIN Clinical Trials Registry (UMIN000046991).