Changes of T Lymphocyte Subsets after CAR-T Cell Therapy and Its Clinical Significance

Introduction: In tumor cell immunity, T cells play a central regulatory role. T cells are divided into several major subsets based on different cell surface molecules to maintain the body's immune balance. Detection of T lymphocyte expression levels can assist in the dynamic analysis of changes in cellular immune function during treatment. CAR-T cell therapy is one of the most promising immune therapies in recent years. The current research focuses on the immune function of CAR-T cells, while ignoring the changes in the body immune system itself. In fact, the body's immune function plays an important role in the anti-tumor immune response, and the changes in the body immune system are likely to be the main reason of long-term maintenance of remission after CAR-T cells exhausted. In our study, we detect the changes of T lymphocyte subsets after CAR-T cell infusion, to explore the effect of CAR-T cell therapy on body immune system and its possible mechanism.

Methods: Peripheral blood of 10 patients after CAR-T cell therapy at different time points were collected. Flow cytometry was used to detect lymphocyte surface molecules including CD3, CAR, CD4, CD8, CD45RA and CCR7 in the scatter plot. T lymphocyte populations were isolated and the ratio of CAR+ and CAR- cells was labeled, and cell subpopulations were labeled in CAR+ and CAR-cells, respectively. Statistical analysis was performed using the R-Studio software package. When comparing the proportion of T cell subsets at different time points, repeated measures of variance analysis were used.

Results: 10 patients with good clinical response and complete data were analyzed and summarized. The proportion of CD8+ cells in CAR+ cell population was (61.4±32.5) % at the initial of CRS, and went up to (74.1±24.5) % as CAR-T cells proliferated to a peak level. After that, CD8+ cells began to decline as CAR-T cells decreased (F= 0.647, P= 0.531). The changes of CD4+ cells went the opposite way (F= 2.678, P= 0.087). The same change patterns of CD8+ and CD4+ cells were shared in CAR- cell population. In CAR+, CAR+CD4+, CAR+CD8+ cell populations, CD45RA+CCR7- cells (effector T cells) have decreased before CAR-T cell peak level. We assumed that effector T cells began to decrease as tumor cells were completely cleared. CD45RA-CCR7-, CD45RA-CCR7+, CD45RA+CCR7+ cells (effector memory T cells, central memory T cells, naïve T cells) gradually increased as the body immune system began to recover. ALL the change patterns were shared in CAR- cells.

Conclusion: The above results suggest that the expansion of CAR-T cells in vivo are mainly CD8+ cells, and are mainly effector T cells that directly exercising killing function. The CAR- cell population shared the same changes of cell subsets with the CAR+ cell population, suggesting that CAR-T cells have certain optimization effects on the body immune system.

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