CD38-Specific but Not CD19-Specific CAR T Cells Exert Anti-Tumor Activity in Models of Primary Effusion Lymphoma (PEL)
Authors: Wang Sisi , Stammler Romain , Richards Rebecca M , Sotillo Elena , Pradier Amandine , Melotti Astrid , Bertoni Francesco , Mackall Crystal L. , Boutboul David , Simonetta Federico 
Published: December 2024

Background. Primary effusion lymphoma (PEL) is a rare form of Human Herpesvirus 8/Kaposi-Sarcoma Herpesvirus (HHV8/KSHV)-related B-cell lymphoma with an aggressive course, usually affecting immunocompromised individuals. Relapsed/refractory PEL has a very poor prognosis and therapeutic options are limited. Chimeric antigen receptor (CAR) T cells have revolutionized the treatment algorithm of diffuse large B-cell lymphoma (DLBCL) but their efficacy in rare lymphomas such as PEL is unknown. PEL usually lacks expression of pan-B-cell markers, such as CD19 and CD20. Conversely, several plasma cell markers, including CD38, are expressed at the surface of the majority of PEL and are currently under investigation as immunotherapy targets. Based on such immunophenotypic characteristics, in this work we tested the hypothesis that CD38-specific but not CD19-specific CAR T cells can exert antitumor effects against PEL.
Methods. We employed two well established models of PEL (KSHV+EBV- ISI and BCP1 cell lines) as well as the DLBCL cell line DoHH2, showing a germinal genter phenotype, as reference. CD19 and CD38 expression was determined at protein level by extracellular flow cytometry. CD19 or CD38-specific CAR T cells with CD28 co-stimulatory domain were produced from healthy donors using retroviral vectors. Transduction efficacy was evaluated by CD19 or CD38 protein binding. Tumor cells were co-cultured with CAR T cells at an effector:target ratio of 1:1 after adjusting for transduction efficacy. Longitudinal cell growth was measured by bioluminescence in mCherry/Luciferase transduced cells after normalization to day 0. The percentage of live cells at day 3 was calculated after normalization to non-treated tumor cells. The t-test was used to determine statistical significance.
Results. The PEL cell lines ISI and BCP1 expressed high levels of CD38 while CD19 expression was undetectable. As expected, the DLBCL cell line DoHH2 expressed high levels of both CD19 and CD38. Accordingly to such immunophenotype, CD19 CAR T cells could inhibit the tumor growth of DoHH2 cells while failed to exert any effect on ISI and BCP1 cells. Conversely, CD38-specific CAR T cells were able to control tumor growth of the three cell lines. An analysis conducted at day 3 on experiments performed with CAR T cells generated from 4 different donors showed that CD19 CAR T cells significantly reduced the percentage of DoHH2 live cells while did not affect PEL cell numbers. Conversely, CD38 CAR T cells led to a significant decrease in DoHH2, ISI and BCP-1 cells.
Conclusions. CD38-specific CAR T cells showed in vitro tumor control in PEL models thus circumventing the tumor escape to CD19-specific CAR T cells due to lack of CD19 expression in PEL cells. Experiments to confirm these results in vivo are currently ongoing. Our data support the potential of CD38 CAR T cell development for the treatment of relapsed/refractory PEL.