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Biological characteristics of newly described HIV-1 BG recombinants in Spanish individuals

Pérez-Alvarez, Lucíaa; Delgado, Elenaa; Villahermosa, María Luisaa; Cuevas, María Teresaa; García, Valentinaa; Vázquez de Parga, Elenaa; Thomson, Michael M.a; Prieto, Arturob; Cuevas, Laureanoa; Medrano, Leandroa; Taboada, José A.c; Nájera, Rafaela; and the Spanish Group for Antiretroviral Resistance Studies in Galicia

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aCentro Nacional de Biología Fundamental, Instituto de Salud Carlos III, 28220 Majadahonda, Madrid, Spain; bComplejo Hospitalario Universitario de Santiago de Compostela; 15705 Santiago de Compostela, La Coruña, Spain; and cConsellería de Sanidade e Servicios Sociais, Dirección Xeral de Saúde Pública, Xunta de Galicia, Spain.

Sponsorship: This work was partly funded by grants MBVI 1023/99/2 and SBVI 1090/00/01 from Plan Nacional del SIDA, Ministerio de Sanidad y Consumo, Spain, and by Scientific Agreement with the Government of Galicia, Xunta de Galicia, Spain.

Received: 21 September 2001;

revised: 12 October 2001; accepted: 16 October 2001.

The HIV-1 epidemic in western Europe is dominated by B-subtype viruses, but non-B and intersubtype recombinants are being identified with increasing frequency [1]. Little is known about the biological characteristics of the recombinant viruses and the relationship with their transmissibility and clinical progression [2,3]. The V3 loop of B-subtype viruses has been shown to play a role in the syncytium-inducing (SI) phenotype, viral tropism and in the differential usage of the chemokine receptors (CCR5, CXCR4) [4]. Although all subtypes can use co-receptors CXCR4 or CCR5, some preferences relative to subtypes have been described [5–8].

In general, non-SI variants display low V3 net charge (≤ +4), whereas SI variants emerge late in the disease course and display higher V3 net charges (≥ +5) [9,10].

In order to determine the biological characteristics of the newly described BG recombinants [11–13] we sequenced the V3 loop from plasma RNA of eight BG strains and eight B-subtype viruses as controls, obtained from HIV-1-infected patients who were attending the same hospitals at the time the study was carried out. Moreover, recombinant BG virus was isolated from the peripheral blood mononuclear cells (PBMC) of one patient and its in-vitro biological properties were studied, including the cell tropism, replication capacity, SI and co-receptor usage.

Epidemiological data are shown in Table 1. All patients were native Spanish, except one from Cabo Verde (X-623). The V3 net charge was calculated on the basis of the difference between the number of positively charged amino acid residues, arginine (R) or lysine (K), and the number of negatively charged residues, aspartic acid (D) or glutamic acid (E) [14]. The prediction of SI phenotype and CXCR4 or CCR5 co-receptor usage was made considering the net charge and by analysing the presence of positively charged amino acids within specific positions that have previously been shown to influence the biological in-vitro phenotype: 306, 320 and 324 positions [15,16].

Table 1
Table 1
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Virus isolation and biological characterization from PBMC were performed as previously described [17]. Co-receptor usage was determined by infecting, with cell-free viral stock, the human glioma cell line, U87.CD4, stably expressing a chemokine receptor CCR1, CCR2b, CCR3, CCR5 or CXCR4, and the human osteosarcoma cell line, GHOST, expressing either CCR3, CCR5, CXCR4, BOB/GPR15 or BONZO(STRL33) [18,19]. Cell cultures were observed daily for cytopathic effects, and supernatant was harvested on day 7 for the detection of p24 antigen (Innotest HIV antigen monoclonal antibody; Innogenetics, Zwijndrecht, Belgium). GHOST cells were analysed using a FACScan flow cytometer. The V3 region was sequenced from patient PBMC proviral DNA and from in-vitro HIV-1 primary isolate.

V3 sequences are shown in Table 1. The estimated V3 net charge was +5.1 (with a range of +4 to +6) for BG recombinant strains, and +4 (with a range of +3 to +5) for B subtypes. The presence of a basic amino acid (R) at the 306 phenotype predictive position was observed in three BG recombinants and in three B-subtype V3 sequences. Other basic amino acid substitutions at phenotype-predictive positions were not detected. However, the net charge in the majority of the BG recombinants was predictive of SI/CXCR4, but they lacked phenotype-associated signature amino acids. Similar findings have been described in some subtype-F isolates [20], suggesting that multiple basic substitutions within the V3 loop, associated with an overall net charge, may be a general requirement for generating the SI/CXCR4 phenotype. It should be noted that most BG recombinant sequences showed several characteristic mutations, corresponding to: 308T, 309M, 314V, 315L, 320Q, 327K (Table 1). These changes were not detected in the B-subtype viruses analysed in this study. Moreover, the frequency of these mutations in the B-subtype sequences published in the Los Alamos Data Base is low, being observed at a range of 5–16%. An important aspect will be to determine whether these divergences between the BG recombinant strains and B-subtype viruses will result in biological differences.

One BG recombinant primary isolate (X-421) was obtained from a patient in A1 clinical stage. Its biological characteristics were: rapid/high replication, SI phenotype, and the usage of CCR2b, CCR3, CCR5 and CXCR4 co-receptors. A V3 amino acid sequence, corresponding to proviral DNA obtained from patient PBMC, was compared with those obtained from primary isolate and MT2 cell lysates. The sequences derived from in-vitro samples showed a positively charged amino acid (K) at the 320 position, resulting in a net charge of +7. This mutation was not observed either in proviral DNA from patient PBMC or in plasma RNA, indicating its emergence under culture-selective pressure.

We have described, for the first time, the biological characteristics of the BG recombinant primary isolate. Interestingly, the SI/X4 phenotype was obtained from a patient in the early clinical stage. The follow-up of this patient will allow us to establish whether these findings are associated with a faster progression of the disease.

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The Spanish Group for Antiretroviral Resistance Studies in Galicia

A. Agulla, A. Mariño, Hospital Arquitecto Marcide, Ferrol (La Coruña); S. López-Calvo, J.D. Pedreira, Hospital Juan Canalejo (La Coruña); A. Aguilera, E. Losada, A. Prieto, Complejo Hospitalario Universitario de Santiago (La Coruña); J. Corredoira, M.J. López- Alvarez, A. Rodríguez, Hospital Xeral-Calde (Lugo); M. Bustillo, J. García-Costa, R. Fernández-Rodríguez, Hospital Nuestra Señora del Cristal (Orense); R. Rodríguez, Hospital Provincial Santa María Madre (Orense); C. Miralles, A. Ocampo, Hospital Xeral-Cíes, Vigo (Pontevedra); R. Ojea de Castro, Hospital Montecelo (Pontevedra); L.E. Morano, R. Pérez-Rodríguez, A. Rodríguez, J. Torres, Hospital Meixoeiro, Vigo (Pontevedra); J. Díz, R. Rodríguez.-Real, Hospital Xeral Provincial (Pontevedra).

Lucía Pérez-Alvareza

Elena Delgadoa

María Luisa Villahermosaa

María Teresa Cuevasa

Valentina Garcíaa

Elena Vázquez de Pargaa

Michael M. Thomsona

Arturo Prietob

Laureano Cuevasa

Leandro Medranoa

José A. Taboadac

Rafael Nájeraa

and the Spanish Group for Antiretroviral Resistance Studies in Galicia

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The authors would like to thank Dr José María Hernández Cochón, Conselleiro de Sanidade e Servicios Sociais, and Dra Pilar Farjas Abadía, Directora Xeral de Saúde Pública, Consellería de Sanidade e Servicios Socias, Xunta de Galicia for their support in the development of the study in Galicia. The technical assistance of Milagros Pinilla and Concepción González-Troncoso is gratefully acknowledged.

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© 2002 Lippincott Williams & Wilkins, Inc.


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