The disease course of HIV is varied in perinatally-infected children; those who succumb to terminal illnesses soon after infection are termed as rapid-progressors. Others termed as long-term non-progressors (LTNP) often survive up to 25 years or longer without antiretroviral therapy (ART) [1]. This variability is related to differences in viral biological properties, host genetics and host immune responses [2]. Several immunoregulatory genes – AIDS restriction genes (ARGs) - play a pivotal role in entry of the virus into the host cell [2]. Mutations in these receptors or their ligands, have been associated with natural resistance to HIV-1 and delayed progression of HIV-1 disease [3]. Two HLA-class I alleles, HLA-B*27 and HLA-B*57 have been associated with slower HIV-1 disease progression in adults [4]. Most studies assessing the role of host genetic factors in LTNPs have been carried out on Caucasian or African populations; studies in India are limited [5-7].

Our study aimed at correlating five commonly reported ARGs, CCR5-D32, SDF1-3’A, CCR5-59029G, HLA- B*57 and B*27, with disease progression among perinatally-infected Indian children.

The study participants were selected from a cohort of 165 children living with perinatally-acquired HIV-1 infection obtaining care at the Pediatric Infectious Disease Clinic, St. John’s Hospital, Bangalore. Written informed consent was obtained from the caregivers, and verbal assent was obtained from children ³8 years of age. The study was approved by the Institutional Ethical Review Board at St. John’s Medical College Hospital, Bangalore. Perinatal acquisition of HIV was confirmed by history and documentation of maternal HIV-positive status, and absence of other risk factors of HIV infection acquisition in the child. The following definition was used to screen for LTNPs: ART-naïve, asymptomatic, HIV-1 infection for >10 years, and CD4 T-cell count >500 cells/mm3. Slow progressors (SP) were defined as children who were ART-naïve, asymptomatic, with known HIV-1 infection for >10 years, and CD4 count<500 cells/mm³ [1]. Normal progressors (NP) constituted those children who had HIV-1 infection for less than 10 years with CD4 cell count <500 cells/mm3. The time of onset of HIV infection was considered as the date of birth of the child, and the length of infection was the same as child’s age. Clinical features and CD4 counts were documented for this study, and viral load was performed using Abbott m2000RT Real Time PCR assay. Genomic DNA was extracted from whole blood using QIAmp DNA Blood Mini Kit (Qiagen, US). SDF1-3’A and CCR5-59029G genotypes were identified by PCR-based restriction followed by fragment length polymorphisms (PCR-RFLP) using MspI and BsaBI. CCR5-D32 was amplified by PCR using the primers described previously [8]. HLA-B*57 and B*27 allele polymorphisms were determined by SSPGo-HLA Typing Kits (Biofortuna, Bromborough, UK) as per manufacturer’s instructions.

Among the 165 children who were initially screened, we identified 6% LTNPs and 5% SPs. We also included 12 NPs, and the final study sample consisted of 30 children (14 males). Mean (SD) CD4 absolute count was 482 (397) cells/mm3, and mean (SD) CD4 percentage was 19% (4%). Mean (SD) viral load was 5.3 (0.7) log copies/mL. The majority of the children were asymptomatic, and 5% had minor illnesses that constituted features consistent with WHO Clinical Stage 2 illnesses. Among the NPs, two each had previous WHO clinical stage 3 or 4 conditions, and all were on anti-retroviral treatment (ART).

The clinical features and allelic distribution of ARGs among the three groups is presented in Table I. None of the children had CCR5-D32 deletion; all had wild-type CCR5. Among the SPs and LTNPs together (collectively called "long term survivors" (LTS)), the SDF1-3’A allele was found either in the heterozygous or homozygous form in 44% (8/18). Among NPs, it was found in 25% (3/12) (P=0.279), Similarly, the CCR5-59029G allele was found in 89% (16/18) among LTS and 92% (11/12) among NPs (P=0.804). The HLA-B*57-positive SP was also heterozygous for SDF1-3’A and CCR5-59029G while the HLA-B*57-positive LTNP was homozygous for SDF1-3’A and heterozygous for CCR5-59029G. The HLA-B*27-positive LTNP was also heterozygous for CCR5-59029G.

TABLE I	Clinical, Demographic and Allelic frequency of AIDS Restriction Genes Among Perinatally-infected 

Children Living with HIV-1, Classified Based on Their Rate of Disease Progression

The progression to AIDS was observed to vary widely in our HIV-1-infected pediatric cohort. It is noteworthy that a tenth of all the children being followed in the clinic belonged to the LTNP or slow progressor category.

The prevalence of LTNPs has been reported to be 3% in children of Spanish and Italian origin [9], and 9% in children of Italian origin [10]. These studies demonstrated the occurrence of known ARGs (CCR5-D32 and SDF1-3’A) among LTNPs at low frequencies. Previous studies in India have analyzed the prevalence of ARGs among exposed seronegative HIV-1 populations and healthy controls [6,11]. A study from a French cohort of adults previously reported that the CCR5-D32 and SDF1-3’A along with HLA-genotypes in combination, portray the synergistic effects of ARGs in disease progression [12]. HLA class I alleles have been closely associated with immune control in HIV among humans [13]. The observation that HIV-infected HLA-B*27-positive individuals can mount strong cytotoxic T lymphocyte (CTL) responses against the immunodominant epitope showed that specific HLA class I alleles can influence the outcome of HIV infection [14]. There is also a gag epitope (corresponding to the gag amino acids 240-249) which is the main target of the acute CD8+T-cell response in HIV-infected subjects who have the HLA-B*57 allele [15].