HIV-1-specific CD8 T cell responses in a pediatric slow progressor infected as a premature neonate

We describe the long-term survival of an individual infected with HIV-1 during extrauterine life as a premature newborn. In the absence of viral attenuation in the Nef/LTR structure or significant co-receptor polymorphisms, slow progression was associated with strong HIV-1-specific broadly cross-reactive CD8 T cell responses. HIV-1 infection as early as 25 weeks' gestation may thus result in the development of immune responses that control viral replication and lead to prolonged survival.

Without treatment, HIV-1 infection among infants and children is associated with shortened survival compared with adults [^1,2]. In particular, T cell immaturity and thymic dysfunction during in-utero infection or as a premature infant may result in accelerated disease progression [³]. The mechanisms underlying slow and non-progression are heterogeneous and include viral attenuation, immunological factors and host genetic determinants.

Infection with Nef/long terminal repeat (LTR) region-deleted HIV-1 resulted in slow progression among recipients from the Sydney Blood Bank Cohort [⁴]. In a proportion of slow progressors the maintenance of expansions of memory CD8 T cells targeted towards multiple conserved epitopes might contribute to the asymptomatic state [⁵]. HLA class I alleles exhibiting broad cytolytic responses associated with slower disease progression among Caucasians include HLA-B5701 [⁶] and B27 [⁷]. Slow progressors heterozygous for δ32 CCR5 have reduced surface expression of the CCR5 co-receptor for macrophage-tropic HIV-1 [⁸]. Additional polymorphisms in the CCR5 promoter and point mutations in the gene (3' UTR) for the stromal-derived factor 1α ligand may also modify disease progression [⁹].

We examined the potential mechanisms of prolonged survival in a Caucasian slow progressor. The patient was infected with HIV-1 as a premature newborn at approximately 25 weeks' gestation in 1981, having received multiple blood transfusions. She survived for 18 years unaware of her HIV-1 status. Her past medical history was significant for recurrent and increasingly severe herpes zoster, which first presented at the age of 9 years. The patient denied any other risk factors. At presentation, the absolute number of CD4 cells and viral load in plasma were less than 10 cells/μl and more than 10⁶ copies/ml, respectively.

Full molecular HLA class I typing of genomic DNA was performed [¹⁰]; HIV co-receptor single nucleotide polymorphisms of proviral DNA were characterized by amplification-refractory mutation system-polymerase chain reaction using sequence-specific primers [¹¹]. γ-IFN elispot assays were performed using a panel of previously defined HIV-1 peptides selected on the basis of class I HLA type [¹²]. Tetramers from a B5701-biotinylation substrate motif tagged plasmid template were generated [¹³]. Nested polymerase chain reaction was employed to amplify the Nef/LTR from proviral DNA [^14,15]. The sequence was analysed using principal coordinate analysis and viral epidemiology signature pattern analysis and was deposited in the GenBank nucleotide database (accession number AYO93617).

The full HLA type of the patient was: A1, A3, B0801, B5701, Bw4, Bw6, Cw6, Cw7, DRB1 03, DRB1 11, DRB3/4/5, DR52, DQB1 02, DQB1 0301/4. No polymorphisms in CCR5, stromal-derived factor 1α and CCR2b associated with delayed disease progression were identified. The sequence of polymorphic regions in the promoter included 59353-CT, 59356-C, 59402-GA and 59029-GA. These polymorphisms individually or in combination have not been associated with accelerated or delayed HIV-1 disease progression [⁹].

Phylogenetic analysis of the Nef sequence identified B clade virus. There was no evidence of variations in Nef or the LTR structure that could account for slow progression. Sites associated with myristoylation, MHC class I and CD4 cell downregulation, and SH3 binding were compatible with clade B reference sequences previously analysed for Nef function in vitro. Protein kinase C and P21-activated kinase domains were similarly conserved (Fig. 1). The LTR gene was intact for all regulatory domains. An insertion upstream at the nuclear factor kappa B binding site was noted. Such insertions have little effect on proviral transcription [¹⁵]. Broad cross-reactive HIV-1-specific CD8 T cell reactivities to all B5701 restricted epitopes were noted. A large single population of B5701-restricted CD8 T cells specific for the p24 epitope KAFSPEVIPMF was confirmed by tetramer staining (1.1%). Effector CD8 T cell populations restricted by HLA A3 and B8 towards p17, p24 and Nef epitopes were also detected by γ-IFN release.

Fig. 1Nef

This is the first description of long-term survival with HIV-1 in a patient infected as a premature infant. Despite HIV-1 infection at the equivalent of approximately 25 weeks' fetal life, the patient generated strong broadly cross-reactive CD8 T cell responses that may have controlled viral replication. Further cytolysis studies demonstrated cross-reactive B5701-restricted recognition of cytotoxic T lymphocytes towards A/AC clade variants of the KAFSPEVIPMF consensus epitope [¹⁶]. These clones tolerated a significant degree of sequence variation. Viral control may eventually have been undermined by mutational escape in immunodominant sequences or impaired cytotoxicity [¹⁷] with the downmodulation of key accessory molecules for antigen presentation by Nef [¹⁸] and T cell signalling (CD3ζ and CD28) [¹⁹].

We are uncertain of the mechanism for survival advantage within the context of thymic dysfunction and an immature immune system. However, the allele HLA B5701 may have contributed to delayed disease progression (although B5701 donors who progress at normal rates have been described [²⁰]). The further identification of preserved functional correlates of HIV-1-specific CD8 T cells that contribute to disease non-/slow progression will be important when formulating strategies for immune-based therapies.

Acknowledgements

R.C. is a Medical Research Council Clinical Training Fellow (UK) and S.L.R.J. is an Elizabeth Glaser Scientist of the Pediatric AIDS Foundation.

Sponsorship: H.B. and B.W. were funded by NIAID grant no. Ro1-A1-42555. S.P. was supported by a National Research Service Award (1F32-HD08478-01) from the National Institute of Child Health and Human Development. M.R. was supported by the Fogarty International Center, NIH grant no. 3D43TW00915.