Tolerance induction with gene-modified stem cells and immune-preserving conditioning in primed mice: restricting antigen to differentiated antigen-presenting cells permits efficacy.

Bone marrow (BM) or hematopoietic stem cell (HSC) transplantation is used as curative therapy for hematologic malignancies. Incorporation of gene therapy to drive tolerogenic expression of antigens is a promising strategy to overcome the limited long-term efficacy of autologous HSC transplantation for autoimmune diseases. HSC engraftment and tolerance induction is readily achieved after myeloablative or immune-depleting conditioning regardless of the cellular compartment in which antigen is expressed. It is unclear whether the efficiency of engraftment and tolerance induction is influenced by targeting antigen to specific cellular compartments. This is particularly important when using clinically feasible low-intensity conditioning aimed at preserving infectious immunity in individuals where immunologic memory exists to the autoantigen to be expressed. Here we demonstrate that, under immune-preserving conditions, confining expression of a transgenically expressed antigen to dendritic cells permits stable, long-term engraftment of genetically modified BM even when recipients are immune to the expressed antigen. In contrast, broader expression within the hematopoietic compartment leads to graft rejection and therapeutic failure because of antigen expression in HSCs. These findings are relevant to the clinical application of genetically engineered HSCs and provide evidence that careful selection of promoters for HSC-mediated gene therapy is important, particularly where tolerance is sought under immune-preserving conditions.

Steady-state antigen-expressing dendritic cells terminate CD4+ memory T-cell responses.

CD4(+) T cells are important effectors of inflammation and tissue destruction in many diseases of immune dysregulation. As memory T cells develop early during the preclinical stages of autoimmune and inflammatory diseases, immunotherapeutic approaches to treatment of these diseases, once established, must include the means to terminate memory T-cell responses. Traditionally, it has been considered that, due to their terminally differentiated nature, memory T cells are resistant to tolerance induction, although emerging evidence indicates that some immunotherapeutic approaches can terminate memory T-cell responses. Here, we demonstrate that CD4(+) memory T-cell responses can be terminated when cognate antigen is transgenically expressed in steady-state DC. Transfer of in-vitro-generated CD4(+) memory T cells establishes, in nontransgenic recipients, a stable and readily recalled memory response to cognate antigen. In contrast, upon transfer to mice expressing cognate antigen targeted to DC, memory CD4(+) T cells undergo a phase of limited proliferation followed by substantial deletion, and recall responses are effectively silenced. This finding is important in understanding how to effectively apply immunotherapy to ongoing T-cell-mediated autoimmune and inflammatory diseases.

Triggering of proteinase-activated receptor 4 leads to joint pain and inflammation in mice.

OBJECTIVE: To investigate the role of proteinase-activated receptor 4 (PAR-4) in mediating joint inflammation and pain in mice. METHODS: Knee joint blood flow, edema, and pain sensitivity (as induced by thermal and mechanical stimuli) were assessed in C57BL/6 mice following intraarticular injection of either the selective PAR-4 agonist AYPGKF-NH(2) or the inactive control peptide YAPGKF-NH(2). The mechanism of action of AYPGKF-NH(2) was examined by pretreatment of each mouse with either the PAR-4 antagonist pepducin P4pal-10 or the bradykinin antagonist HOE 140. Finally, the role of PAR-4 in mediating joint inflammation was tested by pretreating mice with acutely inflamed knees with pepducin P4pal-10. RESULTS: PAR-4 activation caused a long-lasting increase in joint blood flow and edema formation, which was not seen following injection of the control peptide. The PAR-4-activating peptide was also found to be pronociceptive in the joint, where it enhanced sensitivity to a noxious thermal stimulus and caused mechanical allodynia and hyperalgesia. The proinflammatory and pronociceptive effects of AYPGKF-NH(2) could be inhibited by pepducin P4pal-10 and HOE 140. Finally, pepducin P4pal-10 ameliorated the clinical and physiologic signs of acute joint inflammation. CONCLUSION: This study demonstrates that local activation of PAR-4 leads to proinflammatory changes in the knee joint that are dependent on the kallikrein-kinin system. We also show for the first time that PARs are involved in the modulation of joint pain, with PAR-4 being pronociceptive in this tissue. Thus, blockade of articular PAR-4 may be a useful means of controlling joint inflammation and pain.