The oxygen-stable hemolysin streptolysin S (SLS) of Streptococcus pyogenes is encoded in part by the pel/ sagA gene product. Antibodies to a synthetic peptide from the C terminus of the Pel/SagA open reading frame inhibited hemolysis mediated by both culture supernatants from multiple M serotypes of S. pyogenes isolates or a commercially available SLS preparation. Analysis of the SLS-mediated hemolytic reaction demonstrated that it was temperature-and concentration-dependent. Like complement-mediated hemolysis it conforms to the prediction of a one-hit mechanism of hemolysis. A number of intermediates in the SLS-mediated hemolysis of sheep erythrocytes could be distinguished. SLS could bind to erythrocytes below 17°C; however, lysis could only occur at temperatures >23°C. Following binding of SLS and washing, a papain-sensitive intermediate could be distinguished prior to insertion of the SLS complex into the erythrocyte membrane, which resulted in formation of a transmembrane pore and led to irreversible osmotic lysis of the cell. These intermediates were similar to those described previously during complementmediated hemolysis.

To date, molecular targets chosen for Ab activation to generate antitumor effector cells have been confined on T cells, such as TCR/CD3, CD28, CD137 (4-1BB), CD134 (OX40), and inducible costimulator. In this report we investigated the immune function of murine tumor-draining lymph node (TDLN) cells after simultaneous Ab targeting of CD3 on T cells and CD40 on APCs. Anti-CD3 plus anti-CD40-activated TDLN cells secreted significantly higher amounts of IFN-γ, but less IL-10, compared with anti-CD3-activated cells. In adoptive immunotherapy, ligation of CD3 and CD40 resulted in the generation of more potent effector cells in mediating tumor regression. Freshly harvested TDLN cells were composed of ∼60% CD3+ T cells, 30–35% CD19+ B cells, 5% CD11c+ dendritic cells (DC), and few CD14+ or NK cells (each <3%). CD40 was distributed predominantly on B cells and DCs. Cell depletion indicated that simultaneous targeting was toward CD3 on T cells and CD40 on APCs, respectively. Elimination of APCs completely abrogated the augmented antitumor responses induced by anti-CD40. Either B cell or DC removal partially, but significantly, reduced the therapeutic efficacy conferred by CD40 engagement. Furthermore, the immunomodulation function of anti-CD40 was associated with its capability to increase IL-12 secretion while inhibiting IL-4 production. Our study establishes a role for CD40 expressed on B cells or DCs in the costimulation of TDLN cells. Eliciting antitumor activity via simultaneous targeting of CD3 on T cells and CD40 on APCs is relevant for the design of effective T cell-based cancer immunotherapy.

Ligation of TCR and CD28 expressed on T cells via mAbs results in activation of T cells capable of tumor destruction in adoptive immunotherapy. In a murine model, the authors examined in vitro activation conditions utilizing plate-immobilized and bead-conjugated mAbs that bind to CD3 and CD28. Bead-activated tumor-draining lymph node (TDLN) cells demonstrated superior cytokine (IFN-gamma, GM-CSF, IL-2, and IL-10) secretion and mediated tumor regression more efficiently compared with plate-activated cells. The bead-activated TDLN cells had a significantly higher percentage of CD4+ cells compared with plate-activated cells. On a per-cell basis, positively selected CD4+ cells activated with bead-coupled or plate immobilized mAbs mediated tumor-specific regression equally. Bead-activated CD4+ TDLN cells demonstrated significantly higher levels of tumor specific IL-2 secretion compared with plate-activated CD4+ cells that may provide helper function to CD8+ effector cells. The antitumor reactivity of bead-activated lymphoid cells depended upon their source. TDLN cells after bead activation were more potent than splenocytes from tumor-bearing hosts in mediating tumor regression in vivo. Bead-activated LN cells and splenocytes from nontumor-bearing hosts demonstrated nonspecific cytokine secretion and minimal efficacy in adoptive immunotherapy. At minimal doses of IL-2, the antitumor reactivity of bead-activated TDLN cells was significantly enhanced. Anti-CD3/anti-CD28 bead activation of tumor-primed T cells represents an efficient method to generate effector cells for immunotherapy.

We have previously described the antitumor reactivity of tumor-draining lymph node (TDLN) cells after secondary activation with antibodies. In this report, we examined the effects of interleukin (IL)-12 and IL-18 on modulating the immune function of antibody-activated murine TDLN cells. TDLN cells were activated with anti-CD3/anti-CD28 monoclonal antibody followed by stimulation with IL-12 and/or IL-18. IL-18 in combination with IL-12 showed a synergistic effect in augmenting IFNγ and granulocyte macrophage colony-stimulating factor secretion, whereas IL-18 alone had minimal effect. Concurrently, IL-18 prevented IL-12–stimulated TDLN cells from producing IL-10. The IL-12/IL-18–cultured TDLN cells therefore manifested cytokine responses skewed towards a Th1/Tc1 pattern. IL-12 and IL-18 stimulated CD4+ TDLN cells and enhanced IFNγ production by CD4+ cells to a greater extent than by CD8+ cells. Use of NF-κB p50−/− TDLN cells suggested the involvement of NF-κB in the IL-12/IL-18 polarization effect. Furthermore, a specific NF-κB inhibitor significantly suppressed IL-12/IL-18–induced IFNγ secretion, thus confirming the requirement for NF-κB activation in IL-12/IL-18 signaling. In adoptive immunotherapy, IL-12– and IL-18–cultured TDLN cells infiltrated pulmonary tumor nodules and eradicated established tumor metastases more efficiently than T cells generated with IL-12 or IL-18 alone. Antibody depletion revealed that both CD4+ and CD8+ cells were involved in the tumor rejection induced by IL-12/IL-18–cultured TDLN cells. These studies indicate that IL-12 and IL-18 can be used to generate potent CD4+ and CD8+ antitumor effector cells by synergistically polarizing antibody-activated TDLN cells towards a Th1 and Tc1 phenotype.