Efficient engulfment of the intact cell corpse is a critical end point of apoptosis, required to prevent secondary necrosis and inflammation. The presentation of "eat-me" signals on the dying cell is an important part of this process of recognition and engulfment by professional phagocytes. Here, we present evidence that apoptotic cells secrete chemotactic factor(s) that stimulate the attraction of monocytic cells and primary macrophages. The activation of caspase-3 in the apoptotic cell was found to be required for the release of this chemotactic factor(s). The putative chemoattractant was identified as the phospholipid, lysophosphatidylcholine. Further analysis showed that lysophosphatidylcholine was released from apoptotic cells due to the caspase-3 mediated activation of the calcium-independent phospholipase A(2). These data suggest that in addition to eat-me signals, apoptotic cells display attraction signals to ensure the efficient removal of apoptotic cells and prevent postapoptotic necrosis.

Reports of spontaneous regressions of metastases and the demonstration of tumor-reactive cytotoxic T lymphocytes indicate the importance of the host's immune system in controlling the devastating course of metastatic renal cell carcinoma. Recent research indicates that immunization with hybrids of tumor and antigen presenting cells results in protective immunity and rejection of established tumors in various rodent models. Here, we present a hybrid cell vaccination study of 17 patients. Using electrofusion techniques, we generated hybrids of autologous tumor and allogeneic dendritic cells that presented antigens expressed by the tumor in concert with the co-stimulating capabilities of dendritic cells. After vaccination, and with a mean follow-up time of 13 months, four patients completely rejected all metastatic tumor lesions, one presented a 'mixed response', and two had a tumor mass reduction of greater 50%. We also demonstrate induction of HLA-A2-restricted cytotoxic T cells reactive with the Muc1 tumor-associated antigen and recruitment of CD8+ lymphocytes into tumor challenge sites. Our data indicate that hybrid cell vaccination is a safe and effective therapy for renal cell carcinoma and may provide a broadly applicable strategy for other malignancies with unknown antigens.

Background: For optimal T cell activation it is desirable that dendritic cells (DCs) display peptides within MHC molecules as signal 1, costimulatory molecules as signal 2 and, in addition, produce IL12p70 as signal 3. IL-12p70 polarizes T cell responses towards CD4 + T helper 1 cells, which then support the development of CD8 + cytotoxic T lymphocytes. We therefore developed new maturation cocktails allowing DCs to produce biologically active IL-12p70 for large-scale cancer vaccine development.

Help for the induction of cytolytic T lymphocytes is mediated by dendritic cells (DC) that are conditioned by CD40 signaling. We identified tumor necrosis factor family member CD27L͞CD70, which is expressed by cytolytic T lymphocytes on interaction with DC to control CD154 (CD40L) up-regulation on CD45RA؉ helper T cells for subsequent DC stimulation. The results show that the initiation of a cytolytic immune response is determined by regulatory circuits, requiring simultaneous activation and differentiation of all cells involved in T lymphocyte-DC cluster formation.On activation in the periphery, early dendritic cells (DC) differentiate and move antigen into draining lymph nodes. During this process, DC lose their capacity to capture antigen. However, after maturation, DC up-regulate plasmamembrane class II molecules loaded with antigenic fragments, forming stable peptide͞major histocompatibility complexes (MHC) capable of stimulating T cells (1-3). In T cell-rich areas of lymph nodes, DC rapidly cluster with an abundant number of T lymphocytes to initiate or to anergize specific T cell responses (4).DC excel at processing and presenting exogenous viral, bacterial, tumor, and transplantation antigens in association with class I and class II MHC molecules to cytolytic T lymphocytes (CTL) and helper T cells (Th; ref. 5), and DC form long lasting and high avidity conjugates with T cells that are specific for the antigen presented (6, 7). Thus, the microenvironment for the primary induction of a cytolytic immune response is a multicell complex in which distinct cell types are in close proximity, enabling signaling by surface molecules and short-range lymphokines. Recent reports indicate that Th are required for cross-priming and efficient induction of specific CTL responses (8). In this respect, the DC is the entity that links and coordinates antigen-specific activation events by presenting epitopes for both Th and CTL (4,9).In spite of its importance, regulatory elements that initiate productive interactions within T lymphocyte-DC clusters are not defined well. Tumor necrosis factor family members CD27L͞CD70 and CD40L͞CD154 are rapidly inducible molecules preferentially expressed by lymphocytes. Although CD70 is expressed on activated, but not on resting, T cells, its ligand CD27 is expressed stably on virtually all CD45RA ϩ and, at lower levels, on the majority of CD45RO ϩ type T cells (10, 11). Disruption of CD27L͞CD70 signaling in mixed lymphocyte reactions as well as in phytohemagglutinin-, anti-CD2-, or anti-CD3-induced T cell stimulations results in abrogation of cytolytic or proliferative responses, thus underscoring the importance of this costimulatory pathway for T cell activation and T-T cell interactions (12). Moreover, recently CD27L͞ CD70 costimulation has been estimated as equal if not superior to CD80͞CD86 signaling in a mouse-tumor model in vivo (13). CD40L͞CD154 is expressed preferentially on activated, but not on resting, Th, and CD40 is expressed highly on professional antigen-presenting ...