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Highlights from the Resistance Workshop

tagline 1998

  • Like last year's discovery of the gag cleavage site mutation for the protease inhibitors (which this year investigators from Virco reported to be found in up to 55% protease resistant clinical isolates), this year saw several papers reporting a 2-3 amino acid insertion between codons 68 and 70 of the RT gene which was associated with multi-nucleoside resistant virus. An Amsterdam group found the 2 amino acid insert conferred phenotypic resistance to 3TC, d4T, ddI and ddC without displaying the corresponding associated mutations. "These viruses might be insensitive to the whole class of nucleoside RT inhibitors which can have major implications for subsequent antiretroviral treatment." And they go on: "Besides, resistance assays focussing only on the currently known resistance associated mutations miss this new resistance profile and will therefore give the incorrect impression that these viruses are still sensitive to nucleoside RT inhibitors."
     
  • Investigators from Glaxo Wellcome (of all people!) showed that individuals with multiple mutations to several NRTIs have an attenuated -- or no -- response to abacavir.
     
  • So-called "baseline polymorphisms" in the protease gene are increasingly reported among protease naïve individuals. In a French study, pre-existing mutations were observed in 8/11 patients, with a mean number of five mutations per patient. In a separate paper (Statens Serum Institut, Denmark), the L63P baseline mutation was associated with an inferior virologic response to therapy (p=0.08).
     
  • A quad mutant to ritonavir (36I-54V-71V-82T) cloned from a clinical isolate was shown to have increased replicative capacity in vitro -- both in the presence and absence of drug. Yet another chink in the armor of that old wild-type-is-wild-type-because-it's-the-most-replicatively-fit saw. Darwin be damned!
     
  • Tom Merigan, Bob Shafer and Sarah Palmer (Stanford) looked at the effect of hydroxyurea and ddI against ddI-resistant isolates as well as the effect of hydroxyurea in combination with other adenosine analogues (i.e., adefovir dipivoxil and PMPA). The concentration of hydroxyurea used was 50 micro-molar. (Clinical equivalent of 500 mg BID.) At this concentration the didanosine IC50 value for WT virus was reduced 8-fold, for MDR HIV was reduced 17-fold and for MNR HIV was reduced 22-fold. The adefovir IC50 was reduced 8-fold, 4-fold and 5-fold, respectively. The PMPA IC50 was reduced 26-fold, 6-fold and 35-fold, respectively. Increasing the HU concentration to 100 micromolar reduced the adefovir and PMPA IC50 values for all three isolates to levels <0.05 micromolar.
     
  • A paper by Hamburg's Jan Van Lundzberg looked at the restoration or preservation of lymph node architecture and found significant differences between those patients treated with PI-containing regimens and those patients treated with only nucleoside combination regimens. The former showed in tact lymph node architecture while the nuke only group did not. This phenomenon is said to not be solely a function of the perhaps superior potency of a PI-containing regimen. Work to investigate the effect of the non-nuke RTIs on lymph node architecture is underway.
     
  • Famed Brigitte Autran's plenary talk was entitled "Immune Restoration with HAART in Established HIV Infection" ("established" because the mean baseline CD4 cell count in her 317 "highly pre-treated" [but PI naive] patients was 47 cells/mm3; mean baseline plasma viral load was about 5 logs or 100,000 copies/mL). After her talk, Giuseppe Pantaleo cautioned the deceivingly coy Autran not to generalize her restorative observations (which now have quite clear limits) to the whole of HIV-infected patients (i.e., less advanced ones). What seemed to rub the ever-incomprehensible (Can't someone send him to an accent reduction workshop?) Vaudois immunologist the wrong way was Autran's conclusion that the "slope" of immune recovery in her cohort was only 10-20% and that she believes that if complete immune restoration is possible it would require 4-8 years (her range, honestly). One of the moderators of the session, either Tom Merigan or Joep Lange, noted that since the immune damage had taken, on average, some 10 years to accumulate, it was not at all surprising to learn that it might take a comparable time period to repair. Giuseppe reported that in his hands, "earlier" patients who were treated for 48 weeks with ABC+AMP have shown "complete recovery" of T cells in both blood and lymph. He did not elaborate -- but the results were recently published in Nature Medicine.
     
  • In a cohort of long-term non-progressors from the ANRS, Autran looked at immune responsiveness to a series of antigens (or epitopes): HIV-gp160, HIV-p24, streptococcus, PPD and candida. When the LTNP were grouped (somewhat arbitrarily) into those with consistently "low" plasma viral loads (<200; mean 50 copies/mL; range 20-170 copies/mL) or variably low/moderate (my language) (mean 11,400 copies/mL; range 210-860,000 copies/mL), only the group of LTNPs with consistently low plasma viral loads showed evidence of an anti-HIV-gp160 and anti-HIV-p24 immune response. À la Bruce Walker, she postulated that the HIV-specific CD4 cells are either eliminated (very early) by CTL or by chronic activation and eventual deletion via apoptosis. She then showed a slide entitled, "Dendritic cells can rescue CD4+ T cell responses against recall and HIV antigens in LTNPs." She questioned whether the T cell responses (in these LTNPs) against HIV are truly effective or merely markers for disease progression. (Autran appears to believe they are merely markers.) During the discussion the questioned was posed, "Do you believe recovery of the HIV-specific immune response would be faster in earlier patients?" Autran said that they had a cohort of patients who were treated (with HAART?) during primary infection and that no recovery of the HIV-specific CD4 response was seen. [At this point Franco Lori got up (again) to tell us that in his ddI+HU study 6 of 12 (50%) patients, after 2 1/2 years of treatment, had recovered their HIV-specific T helper response. This, he said, has been conducted in collaboration with Bruce Walker. Guiseppe said that in his experience 40-50% of patients treated within 3-6 months of infection get "some recovery" of HIV-specific T help. Franco said that in his study of ddI+HU+IDV 90% of patient have recovered their HIV-specific CD4 cell response. "If we treat later than that," he warned, "we lose everything."]
     
  • Gladstone's Joseph (Mike) McCune presented a great plenary talk about T cell production and the relative contribution to this of the thymus. Using computerized tomography, radio labeled cells and an ultra mod "stable isotope/FACS/GC-MS Technique (see PNAS 2/98 for complete details), McCune looked at the association between evidence of "abundant thymic mass" and age and baseline CD4 T cell count. In what was one of the few encouraging papers of the 4 day summit, McCune showed that while age did have an effect on the ability to detect abundant thymic mass, even at age 39 and older some 50% of volunteers showed evidence of "abundant thymic mass." In those 39 and younger (with baseline CD4 T cell counts 300-500), he saw evidence of thymic function in a full 90% of individuals.
     
  • Australia's Don Smith seems to have done the Bruce Walker experiment (Actually, Giuseppe, Brigitte, and Franco -- and undoubtedly others -- will soon have data to share with us) treating patients with acute seroconversion with various HAART regimens in order to try to preserve the HIV-specific CD4 T cell response and either abort the infection or turn patients into long-term non-progressors. Smith studied 33 acute seroconverters, 16 who were treated and 17 who were not. There were no Western blot bands in 5 and 8 or these patients, respectively; "most" were p24 antigen positive; and the duration of seroconversion symptoms were 19 days in the treated group and 8 days in the non-treated group. Median follow-up was just over one year (56 weeks). Smith and colleagues looked at memory and naïve CD4 and CD8 T cells. In the treated patients they saw a rapid drop off in CD8+ T cell activation -- which falls but does not go back to normal (as it does in Epstein-Barr virus infection, for example). Smith believes this is probably evidence of continued presence of antigen -- but that it could also be that the CD38+HLA-DR+ cell population is simply slow to recover. An important distinction was made between continued "presence" of antigen and continued "replication" of virus. And it remains to be seen which accounts for the continued elevation in activated CD8+ T cells. Smith concluded that aggressive treatment during (or prior to) seroconversion may be able to change rapid progressors into slow progressors but not into HIV negative. Maybe there is no "morning after" afterall.
     
  • Where you might have expected reports of reservoirs and flushing plans -- ways to identify privileged sites and ways to expedite the turn-over of Finzi, Wong and Chun's (a.k.a. Siliciano, Richman, Fauci) now notorious 3rd compartment -- the "eradication" session of this meeting was composed only of three papers contradictorily concluded that 1) No, there is no evidence of viral evolution in these latently infected CD4+ memory T cells; and 2) Yes, there is evidence of viral evolution -- even in patients suppressed to < 20 copies/mL. Sample sizes in all three presentations were small. UCSD's Wong, from Richman's group and the only one to argue against evidence of evolution (Miguel Martinez had 1 patient with evidence of evolution and 2 patients who did not), went at great lengths to explain that his results pertained only to "this certain type of cell" and that he could not say from his data whether or not there might be on-going virus replication in these patients -- occurring in other cell types or other compartments of the body. "I would not make those claims based on these data," he said.
     
  • Franco Lori's latest hydroxyurea presentation was the little-train-that-could which kept chugging up that steep mountainside trying, again in vain, to garner the respect of his fellow investigators. Lori, in collaboration with Bruce Walker, Eric Rosenberg and Judy Lieberman, showed rescue of HIV-specific CD4 T help in 6 of 12 ddI+HU (chronically infected) patients for whom he had long-term (122 weeks) follow-up. "This is the first time this had been reported in chronically infected patients," Lori announced. Charles Boucher immediately jumped up to the mike to challenge Lori with the thought that HU is probably doing nothing antivirally -- not even decreasing the IC50 of ddI-resistant HIV -- but rather simply reducing the number of target cells. Later Andrew Phillips rose to argue that since HU's usefulness (if it has any) is probably not of the virus-inhibiting variety, surrogate marker studies designed to measure antiviral efficacy are not appropriate and that a large, clinical endpoint study is needed.
     
  • Maria Pia De Pasquale of Harvard/Mass General presented the results of ACTG 347: amprenavir+AZT+3TC vs. amprenavir monotherapy. (An earlier version of these results had been presented in Chicago earlier this year.) Of course, AMP looked good in the study, and 15 participants developed mutations associated with reduced sensitivity to other protease inhibitors. (The good news, according to De Pasquale, was that only 4 of the 19 patients on AMP monotherapy developed the I50V amprenavir mutation. The mutations at 10, 20, 46, 82 and 84 which arose seemed to escape her notice.) What's weird and potentially interesting in her abstract -- but not addressed in her oral presentation -- is that 3 of the 7 failures on the triple therapy failed with no signs of genotypic resistance to 3TC or AMP. (All study patients were 3TC and PI naive.) Three additional triple therapy failures showed signs of only 3TC resistance (the M184V mutation). According to the abstract, "this suggests that factors other than drug resistance can initiation failure of triple therapy." Diane Havlir made the same heretical proposition in her updated analysis of ACTG 343: rebound of indinavir sensitive virus while on AZT+3TC+indinavir. While Doug Richman heralded this as necessitating "a fundamental paradigm shift," most of the others who spoke (including Trilege's Françoise Brun-Vezinet) saw nothing odd in this observation.