Weak immunogenicity of chronic lymphocytic leukemia (CLL) cells may contribute to disease progression and inhibit effective immunotherapy. Accordingly, agents that enhance the immunogenicity of CLL cells may be useful in immunotherapeutic approaches to this disease. Since Toll-like receptors (TLRs) are major regulators of innate immunity and initiation of adaptive immunity, we studied the effects of viral pathogen associated molecular pattern agonists (that are recognized by TLRs) on the costimulatory phenotype and function of CLL cells. CLL cells (especially those with high endogenous expression of CD38) responded to TLR7-activating imidazoquinolines and guanosine analogs by increasing costimulatory molecule expression, producing inflammatory cytokines, and becoming more sensitive to killing by cytotoxic effectors. Additional activation of protein kinase C pathways increased the ability to stimulate T-cell proliferation, blocked phosphorylation of the transcription factor, signal transducer and activator of transcription (STAT)3, and resulted in the acquisition of a dendritic cell surface phenotype by TLR7-activated CLL cells. Normal B cells also responded to TLR7 activation by increasing costimulatory molecule expression and cytokine production. These findings suggest a potential role for TLR7 agonists in CLL immunotherapy.

The innate ability of B lymphoma cells to escape control by tumor-reactive T cells must be overcome to develop effective immunotherapies for these diseases. Because signals from both the innate and adaptive immune systems direct the acquisition of strong immunogenicity by professional APCs, the effects of IL-2 and the TLR-7 agonist, S28690, on the immunogenic properties of chronic lymphocytic leukemia (CLL) B cells were studied. IL-2 with S28690 caused CLL cells to proliferate and increased their expression of B7-family members, production of TNF-α and IL-10, and levels of tyrosine-phosphorylated STAT-1 and STAT-3 proteins. S28690 increased CD25 expression on CLL cells and sensitized them to IL-2 signaling. However, IL-2 did not change TLR-7 expression or signaling in CLL cells. The ability to stimulate T cell proliferation required additional activation of protein kinase C, which inhibited tumor cell proliferation, “switched off” IL-10 production, and caused essentially all CLL cells (regardless of clinical stage) to acquire a CD83highCD80highCD86highCD54high surface phenotype marked by the activation of STAT-1 without STAT-3. These findings suggest that TLR-7 “licenses” human B cells to respond to cytokines of the adaptive immune system (such as IL-2) and provide a strategy to increase the immunogenicity of lymphoma cells for therapeutic purposes.

Since the intrinsically poor immunogenicity of chronic lymphocytic leukemia (CLL) cells might be a key factor in allowing them to avoid immune control mechanisms, the development of methods to enhance CLL cell immunogenicity might lead to improved disease control. The ability of CLL cells to stimulate T cells was increased significantly by the protein kinase C (PKC) agonist phorbol myristic acetate (PMA). However, under serum-free conditions, PMA-activated CLL cells died within 48 hours. Antioxidants, such as 2-mercaptoethanol (2-ME), or fetal calf serum could prevent the death of these cells but caused them to enter distinct states of differentiation. In the presence of 2-ME, PMA-activated CLL cells extended dendritic-like protrusions and exhibited increased T-cell stimulatory capacity. In the presence of serum, PMA-activated CLL cells developed fewer dendrites, made less IL-10 and more IL-12 p40 mRNA transcripts, and showed an increased capacity to induce IFN-gamma production by T cells. The effects of serum on the promotion of type 1 immune responses by phorbol ester-activated CLL cells were dominant and correlated with activation of the NF-kappaB signaling pathway. Other PKC agonists, such as Bryostatin-1 and a synthetic Bryostatin analog (Picolog), had similar effects on CLL cells. The observation that CLL cells can acquire features of dendritic cells that promote type 1 immunity may find clinical application in immunotherapeutic strategies for this disease.

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SummaryWeak immunogenicity of chronic lymphocytic leukaemia (CLL) cells may contribute to disease progression and inhibit the effectiveness of immunotherapies, such as vaccines. Agents that can enhance the antigen presenting capabilities of CLL cells might then help to improve the clinical results of immunotherapies. This study investigated the effects of the common gamma chain‐binding cytokines, interleukin (IL)‐2 and IL‐15, on costimulatory properties of primary CLL cells from 51 patients. IL‐2 improved the ability of CLL cells to stimulate T cell proliferation and increased the expression of costimulatory molecules (particularly CD80) in a dose‐dependent fashion, especially in CLL cells with weak expression of CD38. CD80 and CD86 induction by IL‐2 were positively regulated through the mitogen‐activated protein kinase pathway, while CD86 expression was negatively regulated through Janus kinase pathways. However, further activation with protein kinase C agonists was required for IL‐2 activated CLL cells to stimulate autologous T cells sufficiently to clear bystander CLL cells from mixed lymphocyte responses. IL‐15 had similar effects on the costimulatory properties of CLL cells. These results suggest a role for IL‐2, or IL‐15, in immunotherapeutic strategies for CLL.

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Based on their activity in patients with advanced stage chronic lymphocytic leukemia (CLL), a phase I/II study was designed to evaluate the feasibility, safety, and efficacy of autologous vaccines made from oxidized tumor cells in patients with earlier stage CLL, and to determine an optimal schedule of injections. Eighteen patients (at risk for disease progression and with white blood cell counts between 15 and 100 x 10(6) cells/ml) were injected intramuscularly with 10 ml of oxidized autologous blood (composed mainly of CLL cells) either 12 times over 6 weeks (group 1), 12 times over 16 days (group 2), or 4 times over 6 weeks (group 3). Fourteen out of eighteen patients had Rai stage 0-II disease, while 4/18 had stage III-IV disease but did not require conventional treatment. Partial clinical responses, associated with enhanced anti-tumor T cell activity in vitro, were observed in 5/18 patients of whom three were in group 2. Stable disease was observed in six patients while disease progression appeared not to be affected in the remaining patients. Toxicity was minimal. Vaccination with oxidized autologous tumor cells appears worthy of further investigation and may be a potential alternative to a "watch and wait" strategy for selected CLL patients.