TCR-Independent Killing of B Cell Malignancies by Anti–Third-Party CTLs: The Critical Role of MHC–CD8 Engagement

Abstract

We previously demonstrated that anti–third-party CTLs (stimulated under IL-2 deprivation against cells with an MHC class I [MHC-I] background different from that of the host and the donor) are depleted of graft-versus-host reactivity and can eradicate B cell chronic lymphocytic leukemia cells in vitro or in an HU/SCID mouse model. We demonstrated in the current study that human allogeneic or autologous anti–third-party CTLs can also efficiently eradicate primary non-Hodgkin B cell lymphoma by inducing slow apoptosis of the pathological cells. Using MHC-I mutant cell line as target cells, which are unrecognizable by the CTL TCR, we demonstrated directly that this killing is TCR independent. Strikingly, this unique TCR-independent killing is induced through lymphoma MHC-I engagement. We further showed that this killing mechanism begins with durable conjugate formation between the CTLs and the tumor cells, through rapid binding of tumor ICAM-1 to the CTL LFA-1 molecule. This conjugation is followed by a slower second step of MHC-I–dependent apoptosis, requiring the binding of the MHC-I α2/3 C region on tumor cells to the CTL CD8 molecule for killing to ensue. By comparing CTL-mediated killing of Daudi lymphoma cells (lacking surface MHC-I expression) to Daudi cells with reconstituted surface MHC-I, we demonstrated directly for the first time to our knowledge, in vitro and in vivo, a novel role for MHC-I in the induction of lymphoma cell apoptosis by CTLs. Additionally, by using different knockout and transgenic strains, we further showed that mouse anti–third-party CTLs also kill lymphoma cells using similar unique TCR-independence mechanism as human CTLs, while sparing normal naive B cells.

A new approach for eradication of residual lymphoma cells by host nonreactive anti–third-party central memory CD8 T cells

“…These results are similar to our previous results using human cells in which autologous anti-third-party CTLs were found to be effective in eradicating pathological cells. 5,6 In accordance with their human counterparts, the Tcm-induced death of the mouse lymphoma cells was through apoptosis. Thus, the proportion of A20 lymphoma cells binding Annexin V was significantly increased upon interaction with F1 anti-third-party Tcm, from 5.3% 6 2.2% to 14.7% 6 4.5%, respectively ( Figure 1B-C).…”

“…As shown in Figure 2A, Tcm derived from OT-I Rag 2/2 mice induced killing of lymphoma cells (43.9% 6 3%) in comparable levels to that exhibited by nonalloreactive (BALB/ cxB6)F1-derived anti-third-party Tcm (35.3% 6 2.4%), confirming that this killing is indeed TCR independent. To define whether similar to human anti-third-party CTLs, 6 LFA-1, ICAM-1, and CD8 are involved in the killing mechanism, we used blocking Abs. As demonstrated in Figure 2B, preincubation of lymphoma cells with anti-ICAM-1 neutralizing Ab or preincubation of the anti-third-party Tcm with anti-LFA-1 or anti-CD8 neutralizing Ab inhibited the killing by 25.4% 6 3.9%, 59.5% 6 4.4%, and 56.9% 6 2.8%, respectively.…”

“…The possibility that Tcm might exhibit GVL has been indicated initially by our previous unexpected observation in the human setting that both allogeneic and autologous anti-third-party CD8 1 cytotoxic T lymphocytes (CTLs) exhibit in vitro significant killing of B-cell chronic lymphocytic leukemia (B-CLL) 5 and B-cell nonHodgkin lymphoma (B-NHL) cells 6 while sparing acute myeloid leukemia blasts. 5 The killing of B-cell tumors by anti-third-party…”

Immunization with Recombinant Adenoviral Vectors Expressing HCV Core or F Proteins Leads to T Cells with Reduced Effector Molecules Granzyme B and IFN-γ: A Potential New Strategy for Immune Evasion in HCV Infection

“…In these experiments, the GrB levels were very low, and there was no significant difference in different groups (data not shown). This is not surprising in light of the literature from several mouse experiments as well as clinical trials (6,33,34,47,78,79,82). It is known that T cells need to be cultured in vitro with APCs and relevant antigen in order to allow proliferation, expansion, and enrichment of antigenspecific T cells.…”

“…It is known that T cells need to be cultured in vitro with APCs and relevant antigen in order to allow proliferation, expansion, and enrichment of antigenspecific T cells. In clinical trials with various viral and cancer vaccines, antigen-specific CTL activity has invariably been shown with cells cultured in vitro for 4-5 days in the presence of antigen and autologous APCs (47,79,82). It is well-known that in vitro culture with specific antigens allows antigen-specific T cells to expand and/or be enriched, whereas non-specific T cells will die.…”