End Point Considerations for Clinical Trials in Enteric Hyperoxaluria.

Enteric hyperoxaluria is a medical condition characterized by elevated urinary oxalate excretion due to increased gastrointestinal oxalate absorption. Causative features include fat malabsorption and/or increased intestinal permeability to oxalate. Enteric hyperoxaluria has long been known to cause nephrolithiasis and nephrocalcinosis, and, more recently, an association with CKD and kidney failure has been shown. Currently, there are no US Food and Drug Administration-approved therapies for enteric hyperoxaluria, and it is unclear what end points should be used to evaluate the efficacy of new drugs and biologics for this condition. This study represents work of a multidisciplinary group convened by the Kidney Health Initiative to review the evidence supporting potential end points for clinical trials in enteric hyperoxaluria. A potential clinical outcome is symptomatic kidney stone events. Potential surrogate end points include ( 1 ) an irreversible loss of kidney function as a surrogate for progression to kidney failure, ( 2 ) asymptomatic kidney stone growth/new stone formation observed on imaging as a surrogate for symptomatic kidney stone events, ( 3 ) urinary oxalate and urinary calcium oxalate supersaturation as surrogates for the development of symptomatic kidney stone events, and ( 4) plasma oxalate as a surrogate for the development of the clinical manifestations of systemic oxalosis. Unfortunately, because of gaps in the data, this Kidney Health Initiative workgroup was unable to provide definitive recommendations. Work is underway to obtain robust information that can be used to inform trial design and medical product development in this space.

End Points for Clinical Trials in Primary Hyperoxaluria.

Patients with primary hyperoxaluria experience kidney stones from a young age and can develop progressive oxalate nephropathy. Progression to kidney failure often develops over a number of years, and is associated with systemic oxalosis, intensive dialysis, and often combined kidney and liver transplantation. There are no therapies approved by the Food and Drug Association. Thus, the Kidney Health Initiative, in partnership with the Oxalosis and Hyperoxaluria Foundation, initiated a project to identify end points for clinical trials. A workgroup of physicians, scientists, patients with primary hyperoxaluria, industry, and United States regulators critically examined the published literature for clinical outcomes and potential surrogate end points that could be used to evaluate new treatments. Kidney stones, change in eGFR, urine oxalate, and plasma oxalate were the strongest candidate end points. Kidney stones affect how patients with primary hyperoxaluria feel and function, but standards for measurement and monitoring are lacking. Primary hyperoxaluria registry data suggest that eGFR decline in most patients is gradual, but can be unpredictable. Epidemiologic data show a strong relationship between urine oxalate and long-term kidney function loss. Urine oxalate is reasonably likely to predict clinical benefit, due to its causal role in stone formation and kidney damage in CKD stages 1-3a, and plasma oxalate is likely associated with risk of systemic oxalosis in CKD 3b-5. Change in slope of eGFR could be considered the equivalent of a clinically meaningful end point in support of traditional approval. A substantial change in urine oxalate as a surrogate end point could support traditional approval in patients with primary hyperoxaluria type 1 and CKD stages 1-3a. A substantial change in markedly elevated plasma oxalate could support accelerated approval in patients with primary hyperoxaluria and CKD stages 3b-5. Primary hyperoxaluria type 1 accounts for the preponderance of available data, thus heavily influences the conclusions. Addressing gaps in data will further facilitate testing of promising new treatments, accelerating improved outcomes for patients with primary hyperoxaluria.

Antigen-presenting cells containing multiple costimulatory molecules promote activation and expansion of human antigen-specific memory CD8+ T cells.

We have previously demonstrated that multiple immunizations with vector-based vaccines containing transgenes for tumor Ags and a triad of costimulatory molecules (TRICOM) enhance the expansion and functional avidity of Ag-specific memory CD8(+) T cells in a mouse model. However, the effect of enhanced costimulation on human memory CD8(+) T cells is still unclear. The study reported here was an in vitro investigation of the proliferation and function of CEA-specific human memory CD8(+) T cells following enhanced costimulation. Our results demonstrated that TRICOM costimulation enhanced production of multiple cytokines and expansion of CEA-specific memory CD8(+) T cells. The lytic capacity of memory CTLs toward CEA(+) tumors was also significantly enhanced. IL-2R alpha (CD25) was upregulated dramatically following APC-TRICOM stimulation, suggesting that the enhanced expansion of memory CD8(+) T cells may be mediated by increased expression of IL-2R on memory T cells. The enhanced cytokine production and proliferation following TRICOM signaling was completely blocked by the combination of neutralizing Abs against B7-1, ICAM-1, and LFA-3, the costimulatory molecules comprising TRICOM. No difference in T-cell apoptosis was observed between APC-TRICOM and APC-wild-type groups, as determined by annexin V, Bcl-2, and active caspase-3 staining. Results indicated that enhanced costimulation greatly expanded human CEA-specific CD8(+) T cells and enhanced T-cell function, without inducing increased apoptosis of CEA-specific memory CD8(+) T cells.

Regulatory considerations in development of vaccines to prevent disease caused by Chikungunya virus.

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus. Chikungunya disease (CHIK) in humans is characterized by sudden onset of high fever, cutaneous rash, myalgia and debilitating polyarthralgia. Until recently the virus was considered endemic to only Africa and Asia, but since 2004 CHIK has spread to previously non-endemic regions, including Europe and the Americas, thereby emerging as a global health threat. Although a variety of CHIKV vaccine candidates have been tested in animals, and a few have advanced to human clinical trials, no licensed vaccine is currently available for prevention of disease. In this article, we review recent efforts in CHIKV vaccine development and discuss regulatory considerations for CHIKV vaccine licensure under U.S. FDA regulations. Several licensure pathways are available, and the most appropriate licensure pathway for a CHIK vaccine will depend on the type of evidence that can be generated to demonstrate the vaccine's effectiveness. If "traditional approval" following demonstration of direct benefit in adequate and well-controlled clinical disease endpoint studies is not possible, the Accelerated Approval and Animal Rule pathways are potential alternatives. In terms of vaccine safety, the potential for vaccine associated arthralgia and antibody-dependent enhancement of infectivity and disease severity are important issues that should be addressed in both pre-clinical and clinical studies. CHIK vaccine developers are encouraged to communicate with the FDA during all stages of vaccine development.

Induction of higher-avidity human CTLs by vector-mediated enhanced costimulation of antigen-presenting cells.

The efficacy of antigen-specific CD8(+) CTLs depends not only on the quantity of CTLs generated but also perhaps, more importantly, on the avidity of the CTLs. To date, however, no strategy has been shown to preferentially induce higher-avidity human CTLs. In the present study, antigen-presenting cells (APC) generated from human peripheral blood mononuclear cells were infected with a recombinant avipox vector (rF-) containing the transgenes for a triad of costimulatory molecules (human B7.1, intercellular adhesion molecule-1, and LFA-3, designated as rF-TRICOM) and then used to elicit peptide-specific CTLs from autologous T cells. Compared with peptide-pulsed noninfected APCs or peptide-pulsed APCs infected with wild-type vector, peptide-pulsed APCs infected with rF-TRICOM induced not only more CTLs but also higher-avidity CTLs; this was shown by tetramer staining, tetramer dissociation, IFN-gamma production, and cytolytic assays. Peptide-pulsed rF-TRICOM-infected dendritic cells were also shown to induce CTLs with a >10-fold higher avidity than CTLs induced using CD40L-matured dendritic cells; the use of peptide-pulsed CD40L-matured dendritic cells infected with rF-TRICOM as APCs induced CTLs of even greater avidity. To our knowledge, these studies are the first to show a methodology to induce higher-avidity human CTLs and have implications for the development of more efficient vaccines for a range of human cancers.

Vaccines with enhanced costimulation maintain high avidity memory CTL.

The avidity of Ag-specific CTL is a critical determinant for clearing viral infection and eliminating tumor. Although previous studies have demonstrated that vaccines using enhanced costimulation will enhance the level and avidity of Ag-specific T cells from naive mice, there are conflicting data about the effects of vaccines using enhanced costimulation (vector or dendritic cell based) on the survival of memory T cells. In this study we have first extended previous observations that primary vaccination with a recombinant vaccinia virus (rV-) expressing a model Ag (LacZ) and a triad of T cell costimulatory molecules (B7-1, ICAM-1, and LFA-3 (designated TRICOM)) enhances the level and avidity of T cells from naive vaccinated C57BL/6 (Thy1.2) mice. Adoptive transfer of Thy1.1 memory CD8(+) T cells into naive Thy1.2 C57BL/6 mice was followed by booster vaccinations with a recombinant fowlpox (rF-)-expressing LacZ (rF-LacZ) or booster vaccinations with rF-LacZ/TRICOM. Analysis of levels of beta-galactosidase tetramer-positive T cells and functional assays (IFN-gamma expression and lytic activity) determined that booster vaccinations with rF-LacZ/TRICOM were superior to booster vaccinations with rF-LacZ in terms of both maintenance and enhanced avidity of memory CD8(+) T cells. Antitumor experiments using a self-Ag (carcinoembryonic Ag (CEA) vaccines in CEA transgenic mice bearing CEA-expressing tumors) also demonstrated that the use of booster vaccinations with vaccines bearing enhanced costimulatory capacity had superior antitumor effects. These studies thus have implications in the design of more effective vaccine strategies.

Treatment of melanoma with 5-fluorouracil or dacarbazine in vitro sensitizes cells to antigen-specific CTL lysis through perforin/granzyme- and Fas-mediated pathways.

Several factors may influence sensitivity of melanoma cells to CTL lysis. One is the avidity of the CTL TCR. A second is that certain cytotoxic drugs have been reported to sensitize cancer cells to CTL lysis through Fas-mediated apoptosis. In this study, we examined whether antineoplastic agents 5-fluorouracil (5-FU) and dacarbazine (DTIC) sensitize melanoma cells to lysis of G209 peptide-specific CTL. Our results show that CTL generated from PBMC are HLA-A2 restricted and gp100 specific. Treatment with 5-FU or DTIC sensitized melanoma cells to lysis of G209-specific CTL. Most importantly, 5-FU- or DTIC-treated melanoma cells also became sensitive to low-avidity CTL, which per se are less cytolytic to melanomas. We sought to identify apoptotic pathways mediating this effect. The enhanced cytolysis was mediated through the perforin/granzyme pathway. Although 5-FU up-regulated FasR expression on melanoma cells, sensitization was not blocked by anti-Fas Ab, and the G209-specific CTL was Fas ligand (FasL) negative. However, when G209-specific CTL were stimulated to express FasL, FasL signaling also contributed to enhanced cytolysis. DTIC treatment, which did not increase FasR expression, also sensitized FasL-mediated killing induced by neutralizing anti-Fas Ab. For CD95L-positive G209-specific CTL, the sensitization was primarily mediated through the perforin/granzyme pathway regardless of up-regulation of FasR. The findings demonstrate that cytotoxic drug-mediated sensitization primes both perforin/granzyme and Fas-mediated killing by melanoma-specific CTL. Considering that most of autoreactive antitumor CTL are low avidity, the findings provide experimental basis for understanding cytotoxic and immunologic therapeutic synergy in melanoma.

Antimelanoma activity of CTL generated from peripheral blood mononuclear cells after stimulation with autologous dendritic cells pulsed with melanoma gp100 peptide G209-2M is correlated to TCR avidity.

Anchor residue-modified peptides derived from tumor-associated Ag have demonstrated success in engendering immune responses in clinical studies. However, tumor regression does not always correlate with immune responses. One hypothesis to explain this is that CTL resulting from such immunization approaches are variable in antitumor potency. In the present study, we evaluated this hypothesis by characterizing the activity of tumor-associated Ag-specific CTL. We chose an anchor residue-modified peptide from gp100, G209-2M, and used peptide-pulsed dendritic cells to generate CTL from PBMC of HLA-A2(+) normal donors. The specificities and avidities of the resulting CTL were evaluated. The results demonstrate that CTL generated by G209-2M can be classified into three categories: G209-2M-specific CTL which are cytotoxic only to G209-2M-pulsed targets; peptide-specific CTL which recognize both G209 and G209-2M peptides but not melanomas; and melanoma-reactive CTL which recognize peptide-pulsed targets as well as HLA-A2(+)gp100(+) melanomas. CTL that kill only peptide-pulsed targets require a higher peptide concentration to mediate target lysis, whereas CTL that lyse melanomas need a lower peptide concentration. Increasing peptide density on melanomas by loading exogenous G209 peptide enhances their sensitivity to peptide-specific CTL. High avidity CTL clones also demonstrate potent antimelanoma activity in melanoma model in nude mice. Injection of G209 peptide around transplanted tumors significantly enhances the antitumor activity of low avidity CTL. These results suggest that peptide stimulation causes expansion of T cell populations with a range of avidities. Successful immunotherapy may require selective expansion of the higher-avidity CTL and intratumor injection of the peptide may enhance the effect of peptide vaccines.