Failure of low-dose recombinant human IL-2 to support the survival of virus-specific CTL clones infused into severe combined immunodeficient foals: Lack of correlation between in vitro activity and in vivo efficacy

Abstract

Although CTL are important for control of lentiviruses, including equine infectious anemia virus (EIAV), it is not known if CTL can limit lentiviral replication in the absence of CD4 help and neutralizing antibody. Adoptive transfer of EIAV-specific CTL clones into severe combined immunodeficient (SCID) foals could resolve this issue, but it is not known whether exogenous IL-2 administration is sufficient to support the engraftment and proliferation of CTL clones infused into immunodeficient horses. To address this question we adoptively transferred EIAV Rev-specific CTL clones into four EIAV-challenged SCID foals, concurrent with low-dose aldesleukin (180,000 U/ m 2 ), a modified recombinant human IL-2 (rhuIL-2) product. The dose was calculated based on the specific activity on equine PBMC in vitro, and resulted in plasma concentrations considered sufficient to saturate high affinity IL-2 receptors in humans. Despite specific activity on equine PBMC that was equivalent to recombinant equine IL-2 and another form of rhuIL-2, aldesleukin did not support the engraftment and expansion of infused CTL clones, and control of viral load and clinical disease did not occur. It was concluded that survival of Rev-specific CTL clones infused into EIAVchallenged SCID foals was not enhanced by aldesleukin at the doses used in this study, and that in vitro specific activity did not correlate with in vivo efficacy. Successful adoptive immunotherapy with CTL clones in immunodeficient horses will likely require higher doses of rhuIL-2, co-infusion of CD4+ T lymphocytes, or administration of equine IL-2.

Selection of a Rare Neutralization-Resistant Variant following Passive Transfer of Convalescent Immune Plasma in Equine Infectious Anemia Virus-Challenged SCID Horses

“…Initial diagnosis of SCID was based on persistent lymphopenia (Ͻ1,000 peripheral blood lymphocytes [PBL] per l) (32,33) and was confirmed by identification of the homozygous mutation in the DNA-PKcs gene sequence (55). SCID foals were maintained as described previously (33,36,45) with some modifications. For the first 24 to 48 h of life, SCID foals were housed in individual box stalls with their dams to allow ingestion of colostrum.…”

“…For comparisons of the percentages of days that the plasma viral load was Ͼ10,000 RNA copies/ml and of the percentages of days of thrombocytopenia between experimental SCID foals and controls, a t test with Welch correction for unequal variances was used with a two-tailed significance level for ␣ of 0.05. A viral load value of Ͼ10,000 RNA copies/ml was chosen for comparison because clinically apparent infection with fever and declining platelet counts associated with this viral load are consistently observed in EIAV-infected horses (36)(37)(38), and a viral load set point at this level distinguishes between EIAV progressor and nonprogressor horses (24). Statistical analyses were performed using GraphPad InStat, version 3.06, and GraphPad Prism, version 5.01 (GraphPad Software, San Diego, CA).…”

Protective Effects of Broadly Neutralizing Immunoglobulin against Homologous and Heterologous Equine Infectious Anemia Virus Infection in Horses with Severe Combined Immunodeficiency

“…SCID foals were obtained as described previously (5,17,18,27,28,35), and immunocompetent horses A2150 and A2140 were persistently infected with EIAV WSU5 (20). A2150 was the source of immune plasma in our previous study (35), while horse A2140 was the source of immune plasma and PPIg in the current study.…”

Protective Effects of Passively Transferred Merozoite-Specific Antibodies against Theileria equi in Horses with Severe Combined Immunodeficiency

“…Because SCID foals lack functional B and T cells, they provide a powerful and unique opportunity to finely dissect the protective effects of immune interventions against T. equi in the complete absence of other de novo adaptive immune responses. The SCID foals used in this study were obtained by selective breeding of Arabian horses heterozygous for the SCID trait (3,10,11,16). Foals were approximately 1 month of age and included six experimental animals and three control animals.…”