TY  - GEN
CY  - Heidelberg
TI  - The Effect of Elotuzumab on T cells in Patients with Multiple Myeloma
Y1  - 2022///
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/30741/
A1  - Awwad, Mohamed Hemaid Sayed
AV  - public
N2  - Despite recent advances in drug development for cancer immunotherapy, only two monoclonal antibodies have been approved for the treatment of multiple myeloma, among them is elotuzumab, an anti-SLAMF7 antibody. Its mechanism of action has previously been only partly described in terms of NK cell activation and direct antibody dependent cellular cytotoxicity; however, the effect of elotuzumab on T cells has not yet been studied. Therefore, I sought to examine whether SLAMF7 is expressed on T cells, its function in T cells, and the effect of elotuzumab binding to T cells in patients with MM.
I analysed SLAMF7 expression on T cells from patients with MM before and after induction therapy with or without elotuzumab. I also utilized the CRISPR-Cas9 knockout model of SLAMF7 to examine its function and RNA transcriptomic sequencing approach. Moreover, I performed extensive immunological functional analyses to study the effect of the abundance of SLAMF7+ T cells and the immune response on tumour cells.
In the first study, I found that SLAMF7 was expressed on T cells, especially on CD8+ T cells. CD4+ T cells showed modest expression. Thus, I further investigated the immunophenotype of SLAMF7+ CD8+ T cells and found that these cells showed a similar phenotype to CD8+ CD28- CD57+ T cells, a subpopulation previously described by a colleague to exert immunosuppressive capacity to promote tumour growth. Moreover, I found that they expressed high levels of exhaustion markers, indicating that they had an exhausted phenotype as well. Using CRISPR Cas9 knockout model in T cells, I found that there was no significant difference between SLAMF7 knockout and control T cells, suggesting that SLAMF7 is a marker for dysfunction and not an initiator of exhaustion in T cells.
ELISPOT functional assay with T cell from patients showed that patients with a high frequency of CD8+ T cells exhibit weaker anti-tumour cytotoxic activity.   Adding SLAMF7+ CD8+ T cells from myeloma patients suppressed the antigen-specific T cell response of healthy donors T cells in my analyses. Clinically, I found a strong decrease in SLAMF7+ CD8+ T cells after induction therapy in patients who received elotuzumab. Therefore, I hypothesized that elotuzumab might induce antibody dependent cellular phagocytosis a of SLAMF7+ CD8+ T cells. In cooperation with Heiko Bruns at Erlangen University, I found that the majority of SLAMF7+ CD8+ T cells were phagocytosed by autologous phagocytes after adding elotuzumab in vitro. To confirm the finding in vivo, Hakim Echchannaoui at Mainz University and used a similar approach in a myeloma mouse model, and we observed consistent finding. After confirming the cells` depletion mechanism, I also checked for a possible role for natural killer cells in the elimination of T cells but found no evidence. Given these findings, I then investigated how Natural killer cells escape phagocytosis despite expressing SLAMF7 by analysing CD47, which is a phagocytosis-inhibiting (?don?t eat me?) marker, on natural killer cells and comparing it to the expression on T cells. Comparatively, natural killer cells expressed much higher level of CD47 than T cells, highlighting a potential survival advantage against elotuzumab-induced phagocytosis.
In summary, I have shed new light on a key mechanism of action of an anti-SLAMF7 antibody against immunosuppressive CD8+ T cells. Previously, anti-SLAMF7 antibodies were thought to act by targeting myeloma cells directly or by bringing together NK cells and myeloma cells. The findings detailed in my work provide evidence for another therapeutic mechanism. This mechanism, together with the clinical findings, provide a novel potential immune target for the future immunotherapy approaches.
ID  - heidok30741
ER  -