T cell therapies-are T memory stem cells the answer?

Immunotherapeutic Potential of T Memory Stem Cells

Memory T cells include T memory stem cells (T_SCM) and central memory T cells (T_CM). Compared with effector memory T cells (T_EM) and effector T cells (T_EFF), they have better durability and anti-tumor immunity. Recent studies have shown that although T_SCM has excellent self-renewal ability and versatility, if it is often exposed to antigens and inflammatory signals, T_SCM will behave as a variety of inhibitory receptors such as PD-1, TIM-3 and LAG-3 expression, and metabolic changes from oxidative phosphorylation to glycolysis. These changes can lead to the exhaustion of T cells. Cumulative evidence in animal experiments shows that it is the least differentiated cell in the memory T lymphocyte system and is a central participant in many physiological and pathological processes in humans. It has a good clinical application prospect, so it is more and more important to study the factors affecting the formation of T_SCM. This article summarizes and prospects the phenotypic and functional characteristics of T_SCM, the regulation mechanism of formation, and its application in treatment of clinical diseases.

CD8-positive memory T cells in tumor-draining lymph nodes of patients with breast cancer

Background

Human immunological memory is a hallmark of the adaptive immune system and plays an important role in the development of effective immune responses against tumors. In the present study, we aimed to determine the frequencies of CD8⁺ memory T cell subsets including T stem cell memory (TSCM) in tumor-draining lymph nodes of patients with breast cancer (BC).

Methods

Mononuclear cells were obtained from axillary lymph nodes of 52 untreated patients with BC and stained for CD8, CCR7, CD45RO, CD95 markers to detect different subtypes of memory cells in the CD8⁺ lymphocyte population. Data were acquired on four-color flow cytometer and analyzed with CellQuest Pro software.

Results

We observed that 47.65 ± 2.66% of CD8⁺ lymphocytes expressed the CD45RO, a marker for memory T cells. Statistical analysis showed that the total frequency of central memory T cells (TCM) and their subset with low CD45RO expression was significantly higher in tumor-involved nodes compared to tumor-free ones (P = 0.024 and P = 0.017, respectively). The level of CD95 expression (based on mean fluorescence intensity) on the surface of TCM, their CD45RO^hi and CD45RO^low subsets, and TSCM was higher in patients with stage II compared to those in stage I (P < 0.05). In addition, the percentage of naive CD8⁺ T cells was significantly lower in tumor-involved lymph nodes compared to tumor-free ones (P = 0.025).

Conclusions

Our data collectively indicate no significant differences in the frequencies of CD8⁺ lymphocytes or their memory subsets in tumor-draining lymph nodes of patients with BC. However, the frequency of CD45^low TCM was higher in tumor-involved nodes. Along with a decrease in the frequency of naive T cells, the higher frequency of CD45^low TCM suggests that despite the immune reaction to provide a pool of effective memory cells, it is blocked in early-stage of memory cells’ differentiation (CD45RO^low), probably by tumor-derived suppressive factors. Identifying the molecular and cellular mechanisms behind this suppression can provide invaluable tools for adoptive T cell therapies in cancer.

IL-21 Augments Rapamycin in Expansion of Alpha Fetoprotein Antigen Specific Stem-Cell-like Memory T Cells in vitro

INTRODUCTION

Alloreactive tumor specific T cells are important arsenals of the adaptive immune system in the fight against tumors. However, stem cell-like memory T cells (Tscm) provide the key to effective elimination of tumor cells. Methods for generating these T cell subsets already exist. However, they could be made more efficient. Further, they are expensive and unattainable to the resource poor laboratories. In this regard, we are hereby describing a novel in vitro allogeneic co-culture method for raising allo-restricted tumor specific Tscm cells that we developed.

METHODS

We started by obtaining PBLs that screened negative for HLA-A2 molecules from healthy donors followed by co-culture with T2/AFP cells to generate AFP peptide specific tumor-reactive T cells. Controls, IL-21 and/or rapamycin were applied to samples in 24 well plates. Samples were harvested and stained with anti-human CD3, CD8, CD44, CD62L, and HLA-A2/AFP dimer followed by flow cytometry analysis. Cell viability was measured by Trypan blue exclusion assay. One Way ANOVA and independent t test were used to compare the mean differences among and between groups where P values less than 0.05 were considered significant.

RESULTS

Our results show that rapamycin arrests the differentiation of, and expands AFP specific Tscm cells. Further, the expansion of Tscm cells is augmented in the presence of IL-21.

CONCLUSION

IL-21 and Rapamycin can be used concurrently to raise and maintain antigen specific Tscm cells in vitro for purposes of augmenting immunotherapy strategies against cancers.