Treatment of HIV-1 infection with combination therapy: Antiretroviral agents

ScHNITTMAN SM. Treatment of HIV-1 infection with combination therapy: Antiretroviral agents and biological response modifiers. Can J Infect Dis 1994;5(Suppl A):42A-46A. While nucleoside anUrelrovi ral agenls are effective in delaying disease progression in human immunodeficiency virus (111vinfected individuals. lheir acUvity is limited in magnilude and duralion. Therefore, approaches lo allacking l!IV via combinaUon lherapies have recently been under investigation. In particular, since HIV infection dysregulales and deslroys U,e immune system. il is logical lo develop lherapeutic approaches lhal would bolh reslore U1e immune response and have direct anUviral activily. Preliminary evaluations of U,e combination of Zidovudine wilh inlerferon alpha (IFN-a) have demonslraled enhanced antiviral. anlilumour and immunomodulalory aclivily. Other promising approaches include antiretroviral lherapy with inlerleukin (1L) -2. and IFN-a wilh IL-2. The clinical research perlaining lo lhese combinalions of antirelrovirals and biological response modifiers is reviewed.

T HE IIUMAN IMMUNODEFICIENCY VIRUS TYPE I (HIV-I) infects the CD4+ T helper lymphocyte population, leading to a progressive decline in immunological function and ultimately lo the developmenl of AIDS (1). While both the humoral and cellular arms of the immune system respond lo the presence of HIV-1 infection, the relative contrtbu lion of each component in cont.rolling HlV-1 infection and disease progression remains unclear.
Despile the considerable progress made in understanding the pathogenesis of AIDS, the treatment of HIV-1 infection is still in its infancy. Zidovudine (zov. AZT) remains the current standard therapy (2); however ZDV has lox:icities, is only partially effective. and its duration of benefit is limiled by the development of resistance. These observations support the concept that combination therapy can be used to extend clinical benefits in HIV-infected patienls and to prevent the selection of drug-resistant viral varianls.
Since HIV-1 infection is a viral disease that destroys the immune system, it is logical to look for combination therapeutic approaches that would bolster the immune response in general and againsl HIV-1 specifically. A useful strategy for developing combination drug therapies would be to combine agents U1at. do not share cross-resistance, have different mechanisms of action and have different dose-limiting toxicities.

ANTIRETROVIRAL THERAPY IN COMBINATION WITH INTERFERON FOR PATIENTS WITH HIV-1 INFECTION
Interferon alpha (IF'N-a) has demonstrated antiviral, antitumour and immunomodulating activities. Recombinanl (r) IF'N-a and ZDV have been shown to inhibit synergistically the replication of HIV-1 in peripheral blood mononuclear cells (PBMC) in vitro at. concentrations readily achieved in patienls (3). ZDV and IF'N-a inhibit HIV replication by different. mechanisms. ZDV acts at an early stage of replication by inhibiting 111v reverse transcriptase. IF' N -a acts on lat.er st.ages of viral replication by inhibiting budding of viral particles (and possibly earlier slages as well) .
Many reports have shown that IF'N-a can cause lesions of Kaposi's sarcoma to regress in patients with AIDS (4)(5)(6)(7)(8)(9)(10)(11). Patient characteristics likely lo be associated with a response of Kaposi's sarcoma lesions lo IF' N -a include higher CD4+ T cells and no prior opportunistic inJections or AIDS-related complex (ARC) -like symptoms . The most common side effecls encountered in IF'N-a therapy include 'flu-like symptoms (fever, chills, myalgias, fatigue), leukopenia, thrombocyt.openia and elevated liver enzyme levels.
zov prolongs survival and delays the progression of AIDS and ARC (2). The rationale for the use of ZDV in patients with AIDS has to do with the mechanism of HIV replication rat.her than any specific effecl on AIDSrelated Kaposi's sarcoma. Patients treated with ZDV show decreases in serum HIV p24 antigen. an increase in CD4+ T cell number and partial reversal of skin test.
CAN J INFECT DIS VOL 5 SUPPL A FEBRUARY 1994 e nt of HIV-1 with combination the rapy anergy. The most common side effects encountered in ZDV therapy include nausea, fatigue, anemia and neutropenia (dose-dependent.) and peripheral neuropathy.

PHASE l TRIALS IN PATIENTS WITH AIDS-RELATED KAPOSI'S SARCOMA
Kovacs el al (12) were the first t.o describe the safety. lolerance, therapeutic efficacy and antiviral activity of IF'N-a and ZDV combination therapy in patients with AIDS-related Kaposi's sarcoma, and in HIV-1 infection in general. The authors report.eel the results of a clinical trial of combination therapy with IF'N-a and zov in 39 patients with AIDS-related Kaposi's sarcoma. Patienls received 250, 100 or 50 mg of ZDV every 4 h, six weeks after IF'N-a therapy was initialed al 5 million U/day. IF'N -a dose was then increased every two weeks unW a maximal loleraled dose (MTD) was reached, and then both agents were continued for 12 weeks.
The most common side effects were neutropenia, Urrombocytopenia, hepatic dysfunction and weighl loss. Twenty-two of 39 patienls loleraled 12 weeks of therapy without dose reduct.ion -of these. one had a complete response. and 10 had a partial response. The antiviral responses included six of 22 patients who became culture-negative, and three of six patients with p24 antigenemia who became p24 antigen -negative. The CD4+ T cell counts decreased significantly during Lrealment: 552 to 450 cells/mm 3 over 12 weeks; however. the CD4 remained st.able at 35% .
In a phase 1 trtal, Krown el al (13) gave IF'N-a in combination with ZDV to 41 patients with AIDS-related Kaposi's sarcoma. Patients received 100 or 200 mg ZDV every 4 h and 4.5, 9 or 18 million U/day of IF' N -a for eight weeks. Thirty-four of 38 evaluable patients completed U1e therapy.
The major dose-limiting Loxlcily was neut.ropenia. MTDs for IF'N-a were 4.5 million U/day with 200 mg ZDV, or 9 million U/day wiU1 100 mg ZDV. Antilumour effects were seen in 17 of 37 patienls who had complele or partial regressions, with antilumour responses more common in patients with CD4 counts over 200. Eleven of 1 7 responding patients had sustained tumour regressions for weeks 31 lo 101 during extended lrealment., while six of 17 patients relapsed.
Antiviral effects seen included a progressive increase in the proportion of negative cultures over time. In addition, eight. of nine p24 antigenemic patients became p24 antigen-negative during the study. Immunological effects described included 16 of 21 anergic patients who developed skin test reactivity to at least one antigen during the study. In addition. CD4 counts decreased over eight weeks of sludy.
The authors concluded Lhal combination therapy with IF' N-a and ZDV can be safely administered lo patients with AIDS-related Kaposi's sarcoma, and that the anlitumour and antiviral effects were such that further study was warranted.
In a phase l trial. Fischl el al (14) administered IFN-a and ZDV to 56 patients wilh AIDS-related Kaposi's sarcoma. Patients received IFN-a at 9 , 18 or 27 million U/day and ZDV at 100 or 200 mg every 4 h for eight weeks, followed by a 48-week maintenance period. The mean CD4 count at entry was 185 cel ls/mm 3 . The major toxicities were hematological. with anemia (2 .9 to 3.8 g/dL fall in hemoglobin levels over eight weeks) and neutropenia (44% of patients fell to less than 750 cells/mm 3 [worse wilh high dose ZDV]). as well as hepatotoxicity (3.5-fold rise in transaminase activity in all groups, 10 patients with more than a 10-fold increase at the highest combination dose).
Immunologically, an overall gradual increase in CD4 cell counts was seen . Antiviral effects noted were a p24 antigenemia decrease in 12 of 17 p24 antigen-positive patients. Tumour regressions were seen in 42 to 55% of patien ls, a higher percentage lhan lhat seen in previous studies with IFN-a alone. Resistance to ZDV was studied in four patients. and HIV susceptibility showed no change in these patients during 12 months of treatment.
The authors concluded that the study showed that ZDV enhances the beneficial effects of IFN -a in the treatment of AJDS-related Kaposi's sarcoma. In addition, IFN-a may delay the development of ZDV resistance.

PHASE l TRIALS IN ADVANCED HIV-1 INFECTION
In another phase 1 trial, Berglund et al (15) studied 18 patients with symptomatic HIV infection (Centers for Disease Control and Prevention group IV) . All patients were on ZDV (four to 28 months) wilh p24 antigenemia and CD4 mean cell count of approximately 150 cells/mm 3 . In this study. patients received 3 million U/day of native IFN -a for U1ree months, in addition lo continuing ZDV (400 to 1200 mg daily). The toxicities seen included: transient myalgias/art.hralgias. persistent fatigue, hemoglobin decrease from 12.9 to 12.0 g/dL. white blood cell count decrease from 3400 to 2800 cells/mm 3 . platelet decrease from 198.000 to 157.000 cells/mm 3 and weight loss from 68 to 65 kg.
The antiviral effects observed in the study included at least a 70% decrease in 111v culture titres in completely treated patients (8). and significant decrease in p24 antigen in six of eight completely treated patients, but in only one of nine incompletely treated patients. A significant increase in p24 antigenemia in serum was seen after IFN-a treatment was stopped. During IFN-a treatment. CD4 cell counts showed a tendency toward an increased rate of decline.
The conclusions from lhis study were that low dose native IFN -a can exert an antiviral effect even in the absence of a potentiating effect of ZDV in some severely immunocompromised 1-1rv-i.n.fecled patients. Native IFN-a appears to be more likely to induce side effects in combination with ZDV lhan is r!FN -a.
Combination ZDV /IFN-a therapy in patients with ad -44A Y·DO OTCCl'Y vanced 111v-l infection was studied by Edlin et al (16) . Thirteen homosexual men with p24 antigenemia despite six weeks of zov monolherapy were enrolled in an open label dose-ranging pilot trial. Patients continued on zov and were given IFN-a 1.25 lo 7 .5xl0 6 U/m 2 subcutaneously three limes a week. In this study. plasma p24 antigenemia levels demonst.rated a biphasic response, failing initially by a mean of 50% (P=0.001) in 11 patients by 11 weeks. but rising steadily thereafter (P=0.001). CD4+ T cell counts fell by a mean of 7.1 cells/mm 3 /week. Higher initial CD4 counts predicted greater p24 antigenemia reductions. Higher IFN-a doses were associated with more severe side effects and greater falls in CD4 , but no greater reductions in p24 antigenemia. Quantitative polymerase chain reaction for 111v-l DNA in three patients showed a biphasic pattern paralleling the p24 antigenemia response. One can conclude from this study that, although some evidence of short term effects was seen. combination zov /IFN -a showed no lasting antiviral activity beyond that achieved with ZDV alone in patients with advanced 111v-l infection.

LONG TERM FOLLOW-UP IN CLINICAL TRIALS
Long term follow-up of 21 patients with HIV-associated Kaposi's sarcoma treated with zov and JFN -a was reported by Stadler et al (17). Patients received nFN-a 18 million IU every other day with zov 800 lo 1200 mg/day. Fifteen patients tolerated therapy for an average of 10 months (range two to 20). with dose reductions as needed.
In this study. complete remission of Kaposi's sarcoma lesions was seen in four patients, partial remission in three patients, stable disease in two patients and progression in six patients. for an overall response rate of 46%. Even patients wiU1 CD4+ T cell counts under 100 cells/mm 3 responded. In contrast to results of monotherapy wilh IFN-a, patients wilh severely impaired immune systems benefitted from combined treatment with IFN -a and zov.
In summary, lhe phase l /2 clinical trials of ZDV in combination with IFN-a have demonstrated safety and tolerability as well as anlilumour and antiviral effects. In general, the best responses are seen in individuals with CD4 cell counts greater than 200 cells/mm 3 . Randomized, controlled phase 3 trials are underway lo determine this combination's clinical efficacy (18).

ANTIRETROVIRAL THERAPY IN COMBINATION WITH INTERLEUKIN-2 FOR PATIENTS WITH HIV-1 INFECTION
Interleukin (!L) -2 is a Jymphokine produced by T cells that has a number ofimmunomodulating effects. which include: • activation and blast transformation of T cells: • stimulation of cyt.olytic activity against a variety of target cells; • enhanced product.ion of Lhe macrophage activating factor IFN-y; • stimulation of B cells to proliferate, differentiate and secrete immunoglobulins; • increased depressed natural killer activity and cytomegalovirus-specific cytotoxicity of lymphocytes from patients with AIDS; • increased circulating lymphocytes in patients with HIV infect.ion. Previous trials of IL-2 alone in patients wilh AIDS or ARC have given resulls ranging from no deteclable immune enhancement (19.20) to encouraging transienl improvements in a number of parameters (21)(22)(23)(24)(25)(26). These preliminary lrials have suggested further studies of IL-2 in the presence of antiviral drugs and/or less advanced HIV disease.
In a recent sludy by Schwartz et al (27), the safety and preliminary efficacy of continuous int.ravenous IL-2 in conjunction with zov was assessed in 27 asymptomatic patienls infected with I-IIV-1. All patients had CD4 cell counts greater than 400 cells/mm 3 . Patients received ZDV 200 mg orally every 4 h for eight weeks, before beginning IL-2 infusions of 0, 1.5, 3.0, 6.0 or 12.0xl0 6 IU/m 2 /day given Monday through Friday for eight weeks.
In this study. all doses of IL-2 in combination with zov were reasonably tolerated (only two of 27 failed lo complete Lherapy), although virtually all patients experienced headache, fever. myalgia, malaise, fatigue, dry skin and gastrointestinal disturbances to varying degrees. Immunologically, signillcant increases in CD4 cell counts were seen after 23 weeks of receiving the IL-2 infusions with zov, however, Lhe effect was transient and was gone by week 4. CD8 cells followed Lhe same trend. With respect to delayed type hypersensitivity, mild decreases in skin lest responses during high dose IL-2 infusion were seen, but returned to baseline aft.er IL-2 was discontinued. This was in contrast to previous reports of low dose IL-2 enhancing skin t.est reactivity. Significant increases in natural killer and lymphokineactivated killer activity were seen at the higher IL-2 doses. Circulating hypodense eosinophils and soluble IL-2 receptors increased more Lhan 10-fold during combination Lherapy. Virologically, no patient who was p24 antigen-negative developed p24 antigenemia.
The authors concluded that the relatively good tolerance, absence of newly detectable p24 antigenemia and CD4 elevations are encouraging for combination therapy with IL-2 and ZDV.

COMBINATION THERAPY WITH IFN -a AND IL-2 FOR PATIENTS WITH HIV-1 INFECTION
In a phase 1 trial, Schnittman et al (28) evaluated Lhe safety /toxicity of combination treatment with IFN-a and rtL-2 in HIV-infected patients having CD4+ T cell counts of more than 200 cells/mm 3 . MTD of bet.ween 5 and 20 million U/day of IFN-a was delennined for 16 patients; after a minimum of two weeks al Lhe MTD, four patients each received in combination one of the following doses of IL-2, given by continuous intravenous infusion over a Lhree-week period: 0.5, 1.0, 2.0 or 3.0 million IU/day. Of Lhe first. 15 patients enrolled, 10 have completed U1e study as planned, and five went off study before receiving IL-2 (four due to toxicity of IFN-a).
Toxicities of combination therapy wilh IFN-a/lL-2 included fatigue/malaise, anemia, t.ransan1inemia and fever. The inmmnological responses observed included transient increases in CD4+ T cell counls and spontaneous lymphocyte blast transformation, particularly wilh the higher doses of IL-2.
Antiviral effects seen included four of five p24 antigenemic patients who became serum p24 antigennegative while receiving IFN-a. No patient developed serum p24 antigenemia while on study. PBMC quantitative microcultures demonstrated decreasing titres wilh IFN-a alone, wilh further decrements seen wilh the combination of IFN-a/lL-2. Two of two patients with Kaposi's sarcoma had significanl tumour regressions.
ll was concluded Lhal an MTD of between 1 and 2 million JU/day ofIL-2 is reasonably loleraled in combination with an MTD of IFN-a for Lhree weeks. The antiviral responses seen appeared lo be enhanced by Lile addition of IL-2.
In conclusion, the need for more effective therapies for 111v infection is self-evident. Therapies Lhal combine agents wilh anliretroviral activity with Lhose Lhat. can reverse the progressive immunosu ppression of IIIV-1 infection appear to be the most logical approach lo treatment.. Promising combination therapies of this type include ZDV /IFN-a, ZDV /IL-2 and IFN-<X/IL-2. Larger conlrolled trials of these combinations in various staged populations of patients are required to determine the clinical uWily of such regimens. The future of combination therapy lies in several direct.ions. Preliminary studies are underway looking al adoptive immunotherapy with expansion and re-infusion of CDB+ cytotoxic T cells specific for HIV with concomitant. IL-2. In addition, sludies are underway e:>..l)loring inhlbilors of so-called 'bad· cytokines in 111v-l infect.ion, namely tumour necrosis fact.or alpha and IL-6. Finally. considerable inleresl in Lherapeutic vaccination has led lo development. of several clinical trials Lhal may suggest that. this approach is essentially one of biological response modifier.