Type-Specific Immunity in HIV-1 Vertically Infected Infants

High frequencies of CTL recognizing laboratory strains of HIV-1 are present in HIV-1 infected adults as early as preseroconversion. The presence of HIV-1 specific CTL during primary infection has been correlated with better control of early viremia and a more delayed onset of CD4 lymphocyte loss. Previous experiments in our laboratory have demonstrated that, unlike HIV-1 infected adults, the majority of vertically infected infants lack CTL which recognize laboratory strains of HIV-1 within the first year of life. ADCC antibody responses against laboratory strains of HIV-1 env gene products are also delayed until at least two years of age. As a possible correlate, disease progression is also more rapid in vertically infected infants. We hypothesized that HIV-1-specific CTL are type-specific in early infancy and that the use of target cells expressing laboratory strain gene products might limit the detection of HIV-1-specific CTL. To address this hypothesis, HIV-1 env genes from early isolates of four infants were PCR amplified, cloned, and used to generate recombinant vaccinia vectors (vv). The frequencies of CTL precursors (CTLp) recognizing env gene products from autologous isolates and the IIIB strain of HIV-1 were measured at time points from early infancy to 19 months using limiting dilution analysis (LDA). ADCC titers were also measured against autologous and IIIB env gene products at 4 time points spanning 2 months to 2 years of age. CTL precursors from 3 of 4 of these patients were specific only for autologous HIV-1 env gene products during the first 6 to 12 months of age. A pattern of CTL responsiveness was observed in these 3 patients in which type-specific CTL precursors observed in early infancy were replaced by cross-reactive, group-specific CTL by 6 to 12 months of age. CTL precursors from a fourth patient at 12 months of age recognized IIIB env and 1 out of 2 envs derived from 2 autologous viral isolates. High titers titers of ADCC antibodies against autologous env were detected in two infants prior to the detection of ADCC antibodies to IIIB. In two other infants, group specific ADCC antibody responses were detected in late infancy. Our results demonstrate that young infants can mount HIV-1 specific CTL and ADCC responses. The ability of young infants to mount cellular immune responses to HIV-1 also provides support for the concept of perinatal vaccination to prevent HIV-1 transmission. Furthermore. the lack of broadly-reactive CTL in early infancy suggests that the use of vaccines based on laboratory strains of HIV-1 may not afford protection from vertical infection

Early HIV-1 Envelope-specific Cytotoxic T Lymphocyte Responses in Vertically Infected Infants

High frequencies of cytotoxic T lymphocyte precursors (CTLp) recognizing HIV-1 laboratory strain gene products have been detected in adults within weeks of primary infection. In contrast, HIV-1–specific CTLp are uncommonly detected in infants younger than 6 mo. To address the hypothesis that the use of target cells expressing laboratory strain env gene products might limit the detection of HIV-1 env-specific CTLp in early infancy, recombinant vaccinia vectors (vv) expressing HIV-1 env genes from early isolates of four vertically infected infants were generated. The frequencies of CTLp recognizing target cells infected with vv-expressing env gene products from early isolates and HIV-1 IIIB were serially measured using limiting dilution followed by in vitro stimulation with mAb to CD3. In one infant, the detection of early isolate env-specific CTLp preceded the detection of IIIB-specific CTLp. CTLp recognizing HIV-1 IIIB and infant isolate env were detected by 6 mo of age in two infants. In a fourth infant, HIV-1 IIIB env and early isolate env-specific CTLp were simultaneously detected at 12 mo of age. These results provide evidence that young infants can generate HIV-1–specific CTL responses and provide support for the concept of neonatal vaccination to prevent HIV-1 transmission. However, the early predominance of type-specific CTL detected in some young infants suggests that the use of vaccines based on laboratory strains of HIV-1 may not protect against vertical infection

p6gag of human and simian immunodeficiency viruses is tolerant to small in-frame deletions downstream of the late domain

Short, unique, in-frame deletions were consistently detected within p6gag sequences obtained over time from three of eight HIV-1-infected long-term nonprogressors (Alexander, L., Weiskopf, E., Greenough, T.C., Gaddis, N.C., Auerbach, M.R., Malim, M.H., O'Brien, S.J., Walker, B.D., Sullivan, J.L., Desrosiers, R.C., 2000. Unusual polymorphisms in Human Immunodeficiency Virus Type 1 associated with nonprogressive infection. J. Virol. 74, 4361–4376). Using PCR mutagenesis, we created 11 mutant forms of SIV239 and 8 mutant forms of HIV-1 NL4-3 with serial 2 amino acid deletions within p6gag downstream of the PTAP late domain. Nine of the 11 SIV239 mutants assembled and released virion particles similar to wild-type, displayed wild-type infectivity, and replicated similar to wild-type SIV239 in cultured cells. Two of the 11 SIV239 mutants, both involving D at position 21, were grossly defective for intracellular gag accumulation and did not replicate detectably in cultured cells. Similar to the 9 SIV239 mutants, 7 of the 8 HIV-1 mutants replicated well in cultured cells. Only the mutant deleted of ES at positions 19 and 20, immediately adjacent to the PTAP sequence, was markedly impaired in its replicative capacity. These results demonstrate an overall high tolerance of SIV and HIV to two amino acid deletions within p6gag downstream of the late domain

Delayed generation of antibodies mediating human immunodeficiency virus type 1-specific antibody-dependent cellular cytotoxicity in vertically infected infants. WITS Study Group. Women and Infants Transmission Study

Human immunodeficiency virus type 1 (HIV-1)-specific antibody-dependent cellular cytotoxicity (ADCC) antibody titers were serially measured from birth to 24 months in the plasma of 14 intrapartum-infected and 10 uninfected infants born to HIV-1-infected women. The mean ADCC antibody titers measured at birth in infected and uninfected infants were similar (10(-3.9) and 10(-4.0), respectively), suggesting that ADCC antibodies did not protect infants from the intrapartum transmission of HIV-1. In infected infants, ADCC titers at birth did not predict subsequent clinical disease course. The active production of HIV-1-specific ADCC antibodies was detected in most infected infants only after 12 months of age, well after the loss of passively acquired maternal ADCC antibody. The delayed production of ADCC antibodies in infancy may account, in part, for the less efficient control of viral replication and more rapid disease progression following vertical infection compared with that in adults

Broadly reactive antibody-dependent cellular cytotoxic response to HIV-1 envelope glycoproteins precedes broad neutralizing response in human infection

To determine if and when the antibody-dependent cell-mediated cytotoxic (ADCC) response of human serum exhibits broad reactivity across HIV-1 strains, multiple sera were tested for their ability to mediate ADCC against target cells infected with recombinant vaccinia vectors expressing envelope genes of HTLV-IIIB or HTLV-IIIRF. These vectors were found to express the envelope glycoproteins of the two HIV-1 strains and so were appropriate targets for ADCC assays. All the HIV-1-positive sera were able to mediate ADCC against both HTLV-IIIB and HTLV-IIIRF envelope-expressing targets at similar titer. In sera from early seroconverters, the ADCC response was again broadly reactive, even in those sera that exhibited strain-specific neutralizing antibody responses. The ADCC response to natural infection with HIV-1 is therefore broadly reactive and precedes the development of a broad neutralizing antibody response. The broad reactivity of HIV-1-specific ADCC responses may be important for protection against cell-associated virus in vaccine development

Deficient human immunodeficiency virus type 1-specific cytotoxic T cell responses in vertically infected children

Cytotoxic T lymphocyte (CTL) responses to human immunodeficiency virus type 1 (HIV-1) gag proteins were studied prospectively in 17 children (12 infected) born of mothers with HIV-1 seropositivity and in five pediatric patients with hemophilia infected by transfusion of HIV-1-contaminated factor VIII concentrate. B lymphoblastoid cells infected with vaccinia virus vectors expressing HIV-1 gag gene products were combined with autologous peripheral blood mononuclear cells to detect circulating CTLs. Effector cells were defined by monoclonal antibody-mediated, complement-dependent cytolysis. Circulating HIV-1 gag-specific cytotoxic responses were detectable in 4 of 5 HIV-1-infected pediatric hemophilic patients, and were similar in magnitude to those previously described in adults. In contrast, circulating HIV-1 gag-specific cytolysis was detectible in only 3 of 12 vertically infected children. Depletion data revealed that the majority of detectible gag-specific cytolysis was CD8 T cell-mediated. No apparent relationships between CD4 T cell counts, CD8 T cells counts, or serum p24 antigen levels and CTL responses were seen. Deficient CTL development may, in part, explain the more rapid onset of symptomatic disease following vertical HIV infection

Limiting dilution analysis of cytotoxic T lymphocytes to human immunodeficiency virus gag antigens in infected persons: in vitro quantitation of effector cell populations with p17 and p24 specificities

The presence of cytotoxic T lymphocytes (CTL) to the gag antigens of human immunodeficiency virus (HIV) has been described in infected populations. We found that the majority of this immune response as measured in bulk CTL assays of unstimulated peripheral blood mononuclear cells (PBMC) is directed against the p24 component of the p55 gag precursor protein. Using limiting dilution analysis of this effector cell population we confirm that the majority of activated gag-specific CTL circulating in the PBMC of infected hemophilic patients are directed at p24 determinants and are present at frequencies of 1/36,000 to 1/86,000 lymphocytes. By performing in vitro stimulation after limiting dilution, the precursor population of gag-specific CTL are characterized and quantitated. HIV gag-specific CTL precursors are identified at frequencies of 1/1700 to 1/17,000 lymphocytes and are made up of cells with both p17 and p24 specificities. No HIV gag-specific CTL precursor cells are identified in the PBMC of HIV-uninfected individuals. These studies demonstrate that CTL directed at both p17 and p24 determinants make up the cellular immune repertoire in HIV-infected individuals but that only the p24-specific CTL are routinely found in an activated state in the circulation

Antibody-dependent cell-mediated cytotoxicity directed by a human monoclonal antibody reactive with gp120 of HIV-1

We used a human monoclonal antibody (MAb; 15e) to identify an antibody-dependent cell-mediated cytotoxicity (ADCC) epitope on HIV-1 gp120. 15e has been shown to recognize a conformation-dependent epitope on gp120 which is important in both CD4 binding and neutralizing of HIV-1 infection. 15e binds to gp120 of HIV-1IIIB but not HIV-1RF. Using a standard ADCC assay, 15e was found to mediate ADCC against cells infected with HIV-1IIIB but not HIV-1RF. 15e did not mediate ADCC against cells with recombinant gp120 bound to surface CD4, indicating that 15e does not mediate innocent bystander ADCC against uninfected CD4 cells. To better define the 15e epitope, we performed ADCC against target cells infected with a vaccinia vector which expresses processed HIV-1IIIB gp160 from which the third variable region was deleted (amino acids, 312-328). MAb 15e efficiently mediated ADCC against cells expressing this altered form of gp120, indicating that this region is not contributing to the conformational epitope defined by 15e. 15e defines an important epitope in the human immune response to HIV-1 infection. Antibodies with 15e-like activity may be useful in immunoprophylaxis or immunotherapy of HIV-1 infection