Dendritic Cells Infected with PoxvIn Vitro iruses Encoding MART-1/ Melan A Sensitize T Lymphocytes In Vitro

Abstract

Dendritic cells (DC) are potent professional antigen-presenting cells that can activate naive T lymphocytes and initiate cellular immune responses. As adjuvants, DC may be useful in enhancing the immunogenicity of tumor antigens and mediating tumor regression. Endogenous expression of antigen by DC offers the potential advantage of allowing prolonged constitutive presentation of endogenously processed epitopes and exploitation of multiple restriction elements for the presentation of the same antigen. In this report, we show that human DC are (a) capable of infection by recombinant poxviruses encoding melanoma-associated antigen (MAA) genes and (b) capable of efficiently processing and presenting these MAA to cytotoxic T cells. In 6/6 HLA A*0201-expressing melanoma patients tested, the virally driven expression of MART-1/Melan A MAA by DC was sufficient to generate CD8+ T lymphocytes that could recognize naturally processed epitopes on tumor cells. In most cases, specific anti-MART-1 reactivity could be detected after a single stimulation. Analysis of epitope dominance revealed that the amino acid sequence recognized by these cytotoxic T lymphocytes (CTL) corresponded to the MART-1(27-35) residues previously shown to be most commonly recognized by cytotoxic T lymphocytes expanded from metastatic melanoma lesions. These data show that the virally driven expression of MAA by DC can be exploited for the efficient induction of clinically relevant cytotoxic T-cell responses. This has clinical implications for active immunization therapy, and currently vaccine trials have been proposed for patients with metastatic melanoma.

Biased epitope selection by recombinant vaccinia-virus (rVV)-infected mature or immature dendritic cells

“…7,8,27 In particular, we observed that this strategy was more efficient than the exogenous pulsing of iDC with saturating levels of relevant epitope. 7,8 The reason for the enhanced efficiency remained unclear, and we postulated that the longer persistence of Ag on the surface of DC due to the prolonged production of antigenic molecules driven by the viral promoters might have been responsible. 8 Surprisingly, however, in the conduct of these studies we noted that rVV-infected DC had very little ability to stimulate generation of IFN-g production by several Agspecific T-cell clones studied (unpublished observation).…”

“…34 Indeed, we have utilized in the past rVV for the in vitro induction of antimelanoma differentiation antigen-specific CTL. 7,8 We, however, noted that MART-1/MelanA-specific immune reactivity was more easily elicited than that of the larger melanoma differentiation antigen gp100. In addition, we observed that the reactivity elicited against MART-1 was almost exclusively limited to the HLA-A*0201-associated MART-1:27-35 epitope, suggesting that the immunogenicity of a protein may not be necessarily expandable to multiple HLA alleles as desired by the whole Ag vaccination approach.…”

“…46 An appealing tactic for Ag delivery includes the induction of Ag expression in DC to combine the pluripotentiality of whole Ag delivery with the costimulatory properties of these professional antigen-presenting cells. 7,[47][48][49][50] The success of these strategies is based on the assumption that the chances of a given molecule to be immunogenic are relatively uniformly distributed across the HLA polymorphism.…”

“…7 Due to the suggested influence of the duration and intensity of Ag stimulation on the fate of T-cell activation, 19,20 we originally postulated that the higher immunogenicity of rVV-induced Ag delivery was due to prolonged expression of MART-1 driven by rVV infection compared with the short permanence of the same epitope after exogenous pulsing. 8 Others, however, have convincingly demonstrated that rVV infection may have a detrimental role on the function of DC by interfering with their maturation Epitope selection in vaccinia-virus-infected dendritic cells D Nagorsen et al and, as a consequence, efficiency of Ag presentation.…”

“…1,2 In natural conditions, DC most likely present exogenous Ag up-take from dead cells. 3,4 However, for therapeutic purposes, endogenous presentation of Ag encoded by viral vectors infecting DC has been proposed in murine 5 and human [6][7][8][9] models. This strategy of Ag delivery can induce human leukocyte antigen (HLA) class I-and class II-associated immune responses and may represent a potent immunization tool inducing prolonged Ag-specific stimulation within cells capable of powerful costimulation.…”