IntroductionThe potential of transfused T lymphocytes as potent immune effectors is well documented. Such a potential was initially discovered in the allogeneic context from the clinical outcome of patients who received bone marrow transplants, where unselected donor T lymphocytes transfused together with hematopoietic precursors were found to be responsible for the graft-versus-host reaction as well as the graft-versus-leukemia effect. 1 Manipulation of this allogeneic effect through infusion of donor lymphocytes was found to induce durable remission in patients with chronic myelogenous leukemia and in patients with acute myelogenous leukemia relapse following allogeneic bone marrow transplantation. 2 Even more impressive was the restoration of viral immunity in immunodeficient patients after the transfer of cytomegalovirus (CMV) 3,4 -or Epstein-Barr virus (EBV) 5-8 -specific T lymphocytes. Unfortunately, attempts to harness the immune potential of T cells against nonviral malignancies apart from in the context of allogeneic transplantation have been largely unsuccessful, with only a few recent exceptions. [9][10][11][12] In contrast, with the limited positive experience using adoptive transfer of lymphocytes, the clinical benefit of antibody treatment is now well documented. Adoptive immunotherapy with mAbs targeting molecules such as CD20 or Her2/Neu recently has shown its capability to produce a clear clinical benefit, 13 and it is thanks to these studies that the clinical pertinence of several antigens as immune therapeutic targets has been established. Such passively acquired antibodies can trigger apoptosis of tumor cells and activate complement-mediated (CDC) or antibody-dependent cellular cytotoxicity (ADCC) in treated patients. For rituximab, an anti-CD20 humanized mAb, several clinical observations suggested that ADCC mediated by Fc␥RIIIa (CD16)-bearing cells is a key mechanism of action. The gene coding Fc␥RIIIa displays a functional allelic dimorphism generating allotypes with either a phenylalanine (F) or a valine (V) residue at amino acid position 158. In vitro, natural killer (NK) cells from donors homozygous for Fc␥RIIIa-158V (VV) bound more human IgG1 and IgG3 than did NK cells from donors homozygous for Fc␥RIIIa-158F (FF). 14 In vivo, Cartron et al recently have shown that the genotype homozygous for Fc␥RIIIa-158V (VV) is associated with a higher clinical response to rituximab in the treatment of follicular non-Hodgkin lymphomas (NHLs). 15 For the anti-Her2/ Neu humanized mAb trastuzumab, which is widely used to treat Her2/neuϩ breast cancer, mechanisms thought to be responsible for the antitumor activity include down-modulation of the receptor, an antiangiogenic effect, complement-dependent cytotoxicity, a direct apoptotic effect, and ADCC. In fact, in a recent pilot study to elucidate the mechanism by which trastuzumab mediates its antitumor effect, Gennari et al observed that patients with complete or partial remission had a higher in situ leukocyte infiltration and a higher capacity to med...

Human memory T cells are comprised of distinct populations with different homing potential and effector functions: central memory T cells that mount recall responses to Ags in secondary lymphoid organs, and effector memory T cells that confer immediate protection in peripheral tissues. In the present study we demonstrate that a proportion of effector memory T cells express FcγRIIIa (CD16), are perforin positive, and directly mediate Ab-dependent cytotoxicity ex vivo. This particular αβ T lymphocyte subset has the morphology of large granular lymphocytes, increases proportionately in vivo during reactive lymphocytosis, and can be detected in vitro among EBV-specific T lymphocytes after stimulation with EBV Ags. Consequently, during a normal immune response, amplification of these effector memory T lymphocytes that are capable of Ab-dependent cytotoxicity may have beneficial or harmful consequences depending on the presence of pathogen- or tissue-specific Abs, respectively.