Donor-lymphocyte infusion following haploidentical hematopoietic cell transplantation with peripheral blood stem cell grafts and PTCy

Donor-lymphocyte infusion (DLI) for relapse following haploidentical hematopoietic cell transplantation (haploHCT) with post-transplant cyclophosphamide (PTCy) has been described in recipients of bone marrow grafts, but not recipients of G-CSF mobilized peripheral blood (PB) grafts. We retrospectively identified patients who underwent DLI following PB-haploHCT with PTCy for relapse, or loss of chimerism (LOC). Twelve patients (57%) received DLI for hematologic relapse/persistent disease, seven (33%) for extramedullary relapse and two (10%) for LOC. Sixteen (76%) received chemotherapy prior to DLI, which did not correlate with response. The most common first dose was 1 × 10⁶ CD3⁺ cells/kg. Two patients developed grade I aGvHD post DLI, one had grade II and two had grade III. One developed mild skin cGvHD 1361 days post DLI. Pre-DLI aGvHD predicted post-DLI aGvHD (P=0.025). Six patients achieved CR after DLI for overt relapse, one achieved full donor chimerism after LOC. Patients with LOC or EM relapse had superior relapse-free survival following DLI (P=0.029). DLI following PB-haploHCT with PTCy is a viable salvage therapy for overt relapse or LOC without a substantial increase in GvHD, and donor lymphocytes may be collected simultaneously with graft collection to facilitate availability in patients at high risk of relapse.

Efficacy and safety of midostaurin in patients with advanced systemic mastocytosis: 10-year median follow-up of a phase II trial

Patients with advanced systemic mastocytosis (SM) (e.g. aggressive SM (ASM), SM with an associated hematologic neoplasm (SM-AHN) and mast cell leukemia (MCL)) have limited treatment options and exhibit reduced survival. Midostaurin is an oral multikinase inhibitor that inhibits D816V-mutated KIT, a primary driver of SM pathogenesis. We conducted a phase II trial of midostaurin 100 mg twice daily, administered as 28-day cycles, in 26 patients (ASM, n=3; SM-AHN, n= 17; MCL, n=6) with at least one sign of organ damage. During the first 12 cycles, the overall response rate was 69% (major/partial response: 50/19%) with clinical benefit in all advanced SM variants. With ongoing therapy, 2 patients achieved a complete remission of their SM. Midostaurin produced a ⩾50% reduction in bone marrow mast cell burden and serum tryptase level in 68% and 46% of patients, respectively. Median overall survival for the entire cohort was 40 months, and 18.5 months for MCL patients. Low-grade gastrointestinal side effects were common and manageable with antiemetics. The most frequent grade 3/4 nonhematologic and hematologic toxicities were asymptomatic hyperlipasemia (15%) and anemia (12%). With median follow-up of 10 years, no unexpected toxicities emerged. These data establish the durable activity and tolerability of midostaurin in advanced SM.

Clonal diversity of recurrently mutated genes in myelodysplastic syndromes

Recent studies suggest that most cases of myelodysplastic syndrome (MDS) are clonally heterogeneous, with a founding clone and multiple subclones. It is not known whether specific gene mutations typically occur in founding clones or subclones. We screened a panel of 94 candidate genes in a cohort of 157 patients with MDS or secondary acute myeloid leukemia (sAML). This included 150 cases with samples obtained at MDS diagnosis and 15 cases with samples obtained at sAML transformation (8 were also analyzed at the MDS stage). We performed whole-genome sequencing (WGS) to define the clonal architecture in eight sAML genomes and identified the range of variant allele frequencies (VAFs) for founding clone mutations. At least one mutation or cytogenetic abnormality was detected in 83% of the 150 MDS patients and 17 genes were significantly mutated (false discovery rate ≤0.05). Individual genes and patient samples displayed a wide range of VAFs for recurrently mutated genes, indicating that no single gene is exclusively mutated in the founding clone. The VAFs of recurrently mutated genes did not fully recapitulate the clonal architecture defined by WGS, suggesting that comprehensive sequencing may be required to accurately assess the clonal status of recurrently mutated genes in MDS.

Allo-SCT conditioning for myelodysplastic syndrome and acute myeloid leukemia with clofarabine, cytarabine and ATG

The application of myeloablative Allo-SCT is limited by its associated morbidity and mortality. Reduced-intensity conditioning regimens attempt to diminish these, but are associated with a higher risk of disease relapse. Given the evidence of activity of clofarabine and cytarabine in myelodysplastic syndrome/acute myeloid leukemia (MDS/AML), we explored a novel reduced-intensity conditioning regimen based on this backbone. Patients received clofarabine 40 mg/m(2) i.v. on days -6 to -2, cytarabine 1 g/m(2) i.v. on days -6 to -2 and anti-thymocyte globulin (ATG) 1 mg/kg on day -4 and 2.5 mg/kg x 2 days on days -3 and -2. Seven patients were enrolled. Their median age was 54 years; three were with MDS and four with AML. The median duration of neutropenia was 14 days and that of thrombocytopenia was 22 days. Toxicities included hand-foot syndrome (57% grade 2), elevated alanine aminotransferase (ALT) (57% grade 3), elevated aspartate aminotransferase (AST) (86% grade 3) and hyperbilirubinemia (29% grade 3-5). No acute GVHD was observed. Enrollment to the trial was halted after three of the first seven patients expired on days +15, +26 and +32. Three of the four surviving patients have relapsed with a median TTP of 152 days. This regimen was not sufficiently immunosuppressive to ensure engraftment, and was associated with substantial morbidity and mortality.

Low dose Vidaza and thalidomide is an effective combination for patients with myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML)

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Vidaza and thalidomide were administered to 29 patients with MDS or AML. Vidaza was given at a dose of 75mg/kg subq × 5 days q28 days and Thalidomide starting at 50mg/day and increasing to 100mg. Therapy was well tolerated. Median age was 70 years, and there were 16 males. Two patients had RA, 2 RARS, 9 RAEB, 4 CMMoL, 10 AML and 2 Unknowns. According to IPSS, 1 had low, 7 had Int-1, 5 had Int-2 and 4 had high risk disease, and 2 unclassified (10 had AML). Eleven patients had normal, 14 abnormal and 4 unknown for cytogenetics. Seven patients went off the study due to disease progression (5) or refused therapy (1), died within a week of treatment initiation (1) while 2 are on the first cycle and too early for evaluation. Twenty-five patients are evaluable for outcome. Ten patients received 5 or more cycles of Vidaza. HI was seen in 14/25 (56%), and stable disease in 6/25 (24%) while 5/25 (20%) had disease progression. Six patients experienced complete remission (CR) and are still receiving therapy (24%), 1 experienced HI-E, 2 HI-ANC, 3 HI-P, and 2 had a bilineage improvement (HI-P and ANC and HI-E and ANC). Of 10 AML patients, three went off study due to disease progression, 1 had stable disease, 6 responded with 4 complete remissions (CR), 1 HI-ANC and 1 HI-P. Interestingly, 6/10 AMLs had a history of prior MDS, 3/6 achieved CR, 2/6 had HI (ANC and platelets) and 1 has stable disease (continuing treatment). Among the 4 de novo AMLs, 1 had CR and 3 showed disease progression. We conclude that a combination of low dose Vidaza and thalidomide is well tolerated, and highly effective therapy for the treatment of patients with MDS as well as AML arising from a prior MDS. The ability to treat secondary MDS as out-patient and achieve such a high response rate represents a paradigm shift in AML therapy.

No significant financial relationships to disclose.

Low-dose (550 cGy), single-exposure total body irradiation and cyclophosphamide: consistent, durable engraftment of related-donor peripheral blood stem cells with low treatment-related mortality and fatal organ toxicity

On the basis of observations of dog models and from earlier studies with humans, we hypothesized that a low-dose (550 cGy) TBI-based conditioning regimen would result in sustained engraftment of HLA-matched sibling peripheral blood stem cells (PBSC) with low treatment-related mortality (TRM) and low serious organ toxicity if the TBI was given as a single dose and at a high dose rate. The regimen included 550 cGy TBI administered as a single dose at 30 cGy/min and cyclophosphamide. Cyclosporine was given as GVHD prophylaxis. Twenty-seven good-risk (acute leukemia in first remission and chronic-phase chronic myelogenous leukemia) and 53 poor-risk (other) patients were accrued. Complete donor engraftment occurred in 93% to 100% of evaluable patients at each scheduled assessment and was durable through 4 years. Mixed chimerism (50% to 98% donor) was observed in 9 patients (11%). Without further intervention, all patients had complete donor engraftment on subsequent assessments. Graft failure did not occur. TRM through at least 2 years was 7% in the good-risk and 19% in the poor-risk diagnostic groups. Grade 4 (fatal) organ toxicity occurred in only 2 patients (2.5%). Other causes of TRM included infection and GVHD. Median follow-up for the surviving patients was 1234 days (range, 780-1632 days). Current status includes 39 patients (49%) alive and in complete remission, 2 alive in relapse, and 39 dead. Relapse occurred in 15% of the good-risk group and 45% of the poor-risk group. The Kaplan-Meier estimates of 3-year disease-free and overall survival of the good-risk group were 77% and 85%, respectively, and of the poor-risk group were 34% and 36%, respectively. Low-dose (550 cGy), single-exposure TBI given at a high dose rate with cyclophosphamide resulted in consistent durable engraftment of HLA-matched sibling PBSC with a low risk of fatal organ toxicity and TRM.

High-dose cyclophosphamide, BCNU, and VP-16 (CBV) conditioning before allogeneic stem cell transplantation for patients with non-Hodgkin's lymphoma

Allogeneic stem cell transplantation (SCT) has been shown to be a curative therapy for some patients with non-Hodgkin's lymphoma (NHL). Total-body irradiation and high-dose cyclophosphamide combinations are the most established conditioning regimens used in this setting. We examined the efficacy and toxicity of cyclophosphamide, BCNU, and VP-16 (CBV) as a suitable chemotherapy-only regimen for NHL patients. In total, 18 patients, median age 42 years, with NHL were treated with CBV followed by allotransplant. Patients had received a median of two prior chemotherapy regimens. Median times to neutrophil and platelet recovery were 19 and 15 days, respectively. Interstitial pneumonitis occurred in one patient. There have been four relapses after a median follow-up of 39 months. Overall, there were four deaths, one because of relapse. The 2-year estimates of relapse-free and overall survival are 56 and 76%, respectively. CBV is a safe and an effective alternative to TBI-containing regimens before allogeneic SCT for NHL.

Low incidence of transplantation-related acute complications in patients with chronic myeloid leukemia undergoing allogeneic stem cell transplantation with a low-dose (550 cGy) total body irradiation conditioning regimen

Although allogeneic transplantation is a curative therapy for chronic myeloid leukemia (CML), treatment-related mortality is still a major cause of posttransplantation mortality, especially for patients older than 40 years. We investigated, in a phase II trial, the role of a low-dose (550 cGy) high-dose rate (35 cGy/min) single-exposure total body irradiation (TBI) conditioning regimen for allogeneic peripheral blood stem cell (PBSC) transplantation in patients with CML. Between June 1997 and August 2000, 30 adult patients with CML underwent cytokine-mobilized allogeneic PBSC transplantation from HLA-matched siblings following administration of cyclophosphamide (60 mg/kg per day intravenously on days -2 and -1) and single-dose TBI (550 cGy delivered at 30 cGy/min on day 0). Cyclosporine A alone was administered for prophylaxis against graft-versus-host disease (GVHD). Median patient age was 47 years (range, 21-63 years), with 23 patients (77%) older than 40 years. The preparative regimen was well tolerated. Grade 4 toxicities and oral mucositis were not observed. Graft failure did not occur. Severe acute GVHD was observed in 5 patients (17%). The median follow-up was 23 months (range, 6-39 months). Cytogenetic or hematologic relapse was detected in 3 patients (10%), 2 of whom subsequently entered remission following a taper of immunosuppression. Nonrelapse mortality occurred in 5 patients (17%), and the Kaplan-Meier estimate of survival at 2 years was 83% (95% confidence interval, 70%-97%). In summary, this low-dose TBI-based preparative regimen resulted in uniform donor engraftment, with markedly reduced organ toxicity and nonrelapse mortality, in this relatively older cohort of patients with CML.

Sudden death among patients with acute promyelocytic leukemia treated with arsenic trioxide

Arsenic trioxide has been shown to be effective in treating acute promyelocytic leukemia (APL), with minimal overall toxicity reported to date. A phase I/II study was initiated in June 1998 using arsenic trioxide for relapsed APL to determine the maximum tolerated or minimal effective dose and to determine the efficacy of treatment at that dose. Ten patients received 1 to 4 monthly cycles of treatment with 0.1 mg/kg per day intravenous arsenic trioxide. Six of 7 patients evaluable for response achieved cytogenetic or molecular complete remission. However, 3 patients died suddenly during the first cycle of treatment. Autopsies obtained on 2 of these failed to identify a cause of sudden death, despite evidence of pulmonary hemorrhage in one. A third patient, for whom an autopsy was not performed, became asystolic and died while on continuous cardiac telemetry. These observations suggest that arsenic trioxide may be significantly or even fatally toxic at doses currently used and that caution is warranted in its use.

Mouse models of acute promyelocytic leukemia

Translocations involving a variety of fusion partners, such as promyelocytic leukemia gene, promyelocytic leukemia zinc finger, nucleophosmin, nuclear matrix protein, and signal transducer and activator of transcription protein 5B, with the retinoic acid receptor alpha gene are commonly associated with development of acute promyelocytic leukemia. Through the development of transgenic mouse models, some retinoic acid receptor alpha translocation fusion proteins have been shown to be capable of initiating acute promyelocytic leukemia development, and dictate the leukemias' responsiveness to retinoic acid. Transgenic mouse models also have identified the influence of reciprocal translocation fusion proteins on acute promyelocytic leukemia development, and have demonstrated that additional mutations can contribute to the development of acute promyelocytic leukemia. In this review, the authors summarize current mouse models of acute promyelocytic leukemia and describe current knowledge about additional genetic alterations that occur during development of acute promyelocytic leukemia in the mouse.

Immune hemolysis involving non-ABO/RhD alloantibodies following hematopoietic stem cell transplantation

We report two cases of severe alloimmune hemolysis after hematopoietic stem cell (HSC) transplant resulting from an anti-Jk(a). The time course of hemolysis and Jk phenotypes of the donor and recipient in the cases reported suggest that the antibody was produced by donor-derived passenger lymphocytes. Retrospective analysis of the blood bank records of all allogeneic HSC transplant patients at Barnes-Jewish Hospital from 1994 to 1999 suggests that the incidence of alloimmune hemolysis due to incompatibilities involving non-ABO or RhD red cell antigens is very low, approximately 1%. In one patient, the duration of hemolysis was shortened significantly by performing red cell exchange at the first sign of intravascular hemolysis.

Treatment of steroid-resistant acute graft-versus-host disease with anti-thymocyte globulin

Acute graft-versus-host disease (aGVHD) is a major cause of mortality after allogeneic stem cell transplantation. Although initial treatment with corticosteroids is effective in the majority of patients, 30--60% develop steroid resistance. Anti-thymocyte globulin (ATG) is commonly used as first-line therapy for steroid resistant (SR) aGVHD. However, data on its efficacy are limited. At two institutions we reviewed the results of treatment with ATG of 58 patients with SR aGVHD. Initial manifestations of aGVHD were treated with 2 mg/kg/day of methylprednisolone (MP). Equine ATG was administered as first-line therapy for SR aGVHD, a median of 9 days (range, 3 to 39) after initiation of MP. At the time of initiation of ATG, IBMTR severity indices B, C and D were observed in 6%, 40% and 54% of patients, respectively. Improvement was observed in 30% of patients treated with ATG. Skin disease was more likely to improve with ATG (79%), while progression of gut and liver aGVHD was observed in 40% and 66% of patients, respectively. Despite initial improvement, 52 patients (90%) died a median of 40 days after ATG therapy from progressive aGVHD and/or infection (74%), ARDS (15%), or relapse (11%). Only six patients (10%), three of whom had aGVHD limited to the skin at the time ATG was administered, are long-term survivors. We conclude that initial improvement of SR aGVHD occurs with ATG in a minority of patients, and very few patients become long-term survivors. Furthermore, this treatment is associated with a high rate of major complications.

Resolution of psoriasis after allogeneic bone marrow transplantation for chronic myelogenous leukemia: late complications of therapy

Treatment of autoimmune disease with bone marrow transplantation (BMT) is under investigation. A few reports of patients undergoing allogeneic BMT for malignant conditions observed the resolution of psoriasis after BMT, with minimal late morbidity. We describe a patient with chronic myelogenous leukemia (CML) whose psoriasis resolved completely after allogeneic BMT. However, the patient's course was complicated by extensive chronic graft-versus-host disease (GVHD), recurrent serious infections, poor performance status and quality of life, and severe disability. The patient died 887 days post transplant due to infectious complications. The potential benefits and risks of treatment of autoimmune diseases with allogeneic BMT are discussed.

Acquired, nonrandom chromosomal abnormalities associated with the development of acute promyelocytic leukemia in transgenic mice

We previously generated a transgenic mouse model for acute promyelocytic leukemia (APL) by expressing the promyelocytic leukemia (PML)-retinoic acid receptor (RARalpha) cDNA in early myeloid cells. This fusion protein causes a myeloproliferative disease in 100% of animals, but only 15-20% of the animals develop acute leukemia after a long latency period (6-13 months). PML-RARalpha is therefore necessary, but not sufficient, for APL development. The coexpression of a reciprocal form of the fusion, RARalpha-PML, increased the likelihood of APL development (55-60%), but did not shorten latency. Together, these results suggested that additional genetic events are required for the development of APL. We therefore evaluated the splenic tumor cells from 18 transgenic mice with APL for evidence of secondary genetic events, by using spectral karyotyping analysis. Interstitial or terminal deletions of the distal region of one copy of chromosome 2 [del(2)] were found in 1/5 tumors expressing PML-RARalpha, but in 11/13 tumors expressing both PML-RARalpha and RARalpha-PML (P < 0.05). Leukemic cells that contained a deletion on chromosome 2 often contained additional chromosomal gains (especially of 15), chromosomal losses (especially of 11 or X/Y), or were tetraploid (P </= 0.001). These changes did not commonly occur in nontransgenic littermates, nor in aged transgenic mice that did not develop APL. These results suggest that expression of RARalpha-PML increases the likelihood of chromosome 2 deletions in APL cells. Deletion 2 appears to predispose APL cells to further chromosomal instability, which may lead to the acquisition of additional changes that provide an advantage to the transformed cells.

Pathologic, cytogenetic and molecular assessment of acute promyelocytic leukemia patients treated with arsenic trioxide (As2O3)

Arsenic trioxide (As2O3) shows great promise as an effective therapy for patients with all-trans retinoic acid (ATRA)-resistant acute promyelocytic leukemia (APL). Little data is available addressing the pathology of As2O3 treated APL and whether the antileukemic mechanism of As2O3 is primarily cytolysis or through stimulation of cell differentiation. In this report, we made a morphologic, cytogenetic, and molecular evaluation of five ATRA-refractory APL patients who were treated with As2O3. Four of the five patients had morphologic responses after one or two cycles of As2O3 treatment. Of the four responders based on bone marrow morphology, two achieved molecular remission (negative RT-PCR for PML- RAR alpha fusion transcripts) by the end of the second and third cycles of As2O3 therapy. Two patients exhibited marked leukocytosis during the first cycle of As2O3, and at that time point the APL cells were largely replaced by the cells showing partial differentiation towards myelocytes with co-expression of CD11b and CD33. Nevertheless, these "myelocyte-like" cells that showed the t(15;17) translocation eventually disappeared with continuous As2O3 therapy. As2O3 treatment appears to be effective therapy for the patients with relapsed APL after the failure of conventional chemotherapy and ATRA therapy. The pathologic findings in these five cases suggest that at low doses As2O3 primarily induces differentiation of the APL cells, generating abnormal myelocytes resembling APL cells treated with ATRA, whereas at higher doses AS2O3 induces marrow necrosis.

Adverse side-effects associated with G-CSF in patients with chronic myeloid leukemia undergoing allogeneic peripheral blood stem cell transplantation

Administration of the myeloid growth factor G-CSF after allogeneic hematopoietic stem cell transplantation is usually well tolerated, and associated with rapid hematopoietic engraftment. We report a high incidence (50%) of side-effects associated with post-transplant G-CSF in patients with chronic phase chronic myeloid leukemia undergoing allogeneic HLA-identical sibling peripheral blood stem cell transplantation. One or more of the following signs and symptoms were observed shortly after the subcutaneous injection of G-CSF: dyspnea, chest pain, nausea, hypoxemia, diaphoresis, anaphylaxis, syncope and flushing. These reactions led to discontinuation of G-CSF in the majority of patients. Predictive factors could not be identified, and the underlying mechanism leading to these reactions is unknown.

Phase I study of paclitaxel in combination with a multidrug resistance modulator, PSC 833 (Valspodar), in refractory malignancies

PURPOSE

To determine the maximum-tolerated dose (MTD), dose-limiting toxicity (DLT), and pharmacokinetics of paclitaxel when given with PSC 833 (valspodar) to patients with refractory solid tumors.

PATIENTS AND METHODS

Patients were initially treated with paclitaxel 175 mg/m(2) continuous intravenous infusion (CIVI) over 3 hours. Subsequently, 29 hours of treatment with CIVI PSC 833 was started 2 hours before paclitaxel treatment was initiated. In this combination, the starting dose of paclitaxel was 52.5 mg/m(2). Paclitaxel doses were escalated by 17.5 mg/m(2) increments for four subsequent cohorts. Each cohort consisted of three patients with the exception of the last cohort, which consisted of six patients. Data for the pharmacokinetics of paclitaxel with and without concurrent PSC 833 administration were obtained.

RESULTS

All 18 patients completed at least one course of concurrent treatment (median, two courses; range, one to six) and were evaluable for toxicity. The MTD for paclitaxel with PSC 833 was 122.5 mg/m(2). Neutropenia was the DLT. All patients had PSC 833 blood concentrations greater than 1, 000 ng/mL before, during, and 24 hours after the paclitaxel infusion. PSC 833 produced small increases in the paclitaxel peak plasma concentrations and areas under the concentration-time curve. However, PSC 833 greatly prolonged the terminal phase of paclitaxel, resulting in plasma paclitaxel concentrations of more than 0.05 micromol/L for much longer than expected. As a result, myelosuppression was comparable to that produced by full-dose paclitaxel given without PSC 833. Of the 16 patients who were assessable for response, one patient experienced a partial response and an additional nine patients experienced disease stabilization after paclitaxel treatment alone.

CONCLUSION

Treatment with paclitaxel 122.5 mg/m(2) as a 3-hour CIVI concurrent with a 29-hour CIVI of PSC 833 results in acceptable toxicity. The addition of PSC 833 alters the pharmacokinetics of paclitaxel, which explains the enhanced neutropenia experienced by patients treated with this drug combination.

A bcr-3 isoform of RARalpha-PML potentiates the development of PML-RARalpha-driven acute promyelocytic leukemia

Acute promyelocytic leukemia (APML) most often is associated with the balanced reciprocal translocation t(15;17) (q22;q11.2) and the expression of both the PML-RARalpha and RARalpha-PML fusion cDNAs that are formed by this translocation. In this report, we investigated the biological role of a bcr-3 isoform of RARalpha-PML for the development of APML in a transgenic mouse model. Expression of RARalpha-PML alone in the early myeloid cells of transgenic mice did not alter myeloid development or cause APML, but its expression significantly increased the penetrance of APML in mice expressing a bcr-1 isoform of PML-RARalpha (15% of animals developed APML with PML-RARalpha alone vs. 57% with both transgenes, P < 0.001). The latency of APML development was not altered substantially by the expression of RARalpha-PML, suggesting that it does not behave as a classical "second hit" for development of the disease. Leukemias that arose from doubly transgenic mice were less mature than those from PML-RARalpha transgenic mice, but they both responded to all-trans retinoic acid in vitro. These findings suggest that PML-RARalpha drives the development of APML and defines its basic phenotype, whereas RARalpha-PML potentiates this phenotype via mechanisms that are not yet understood.

Identification of HIV1 determinants for T lymphoid cell line infection

Determinants responsible for HIV-1 infection of T lymphoid cell lines were identified by functional analysis of chimeric proviral clones derived from T-cell line tropic-(HXB2) and non-T-cell line-tropic isolates (YU2, ADA). Replacement of the HXB2 V3 envelope loop sequence with that derived from YU2 resulted in a virus that is no longer T cell line-tropic. However, the reciprocal replacement using HXB2 V3 loop sequences did not confer upon either ADA or YU2 envelope proteins the ability to infect T cell lines. Furthermore, the resultant viruses were incapable of infection of primary lymphocytes. Single, double, and multiple point mutations made within the V3 loop sequence did not result in change in tropism, although mutations involving residue 275 resulted in a virus that was incapable of infecting primary lymphocytes but retained the ability to infect Jurkat T lymphoid cells. These results suggest that the V3 envelope determinant is necessary for T cell line infection, but other determinant(s) in envelope are also necessary to obtain infectious virus expression.

Role of HIV-1 envelope V3 loop cleavage in cell tropism

The envelope protein is an important determinant of HIV-1 cell-specific tropism. The gp160 envelope precursor proteins from macrophage-tropic or T lymphoid cell line-tropic strains of HIV-1 were expressed in recombinant vaccinia virus-infected cell lines or primary lymphocytes or macrophages. No significant differences in the kinetics of synthesis of gp160, processing into gp120 and gp41 proteins, N-linked glycosylation, or release of gp120 into the medium were noted with the different envelope proteins. However, gp120 envelope protein shed into the medium was found to be at least partially cleaved at a site within the V3 loop. The gp120 envelope proteins from macrophage-tropic isolates exhibited lower rates of cleavage than those from lymphoid cell line-tropic strains in all cell types examined. Cell-free protease digestion studies also demonstrated relative resistance of the envelopes from macrophage-tropic compared to lymphoid cell line-tropic strains. All recombinant envelope proteins were recognized by monoclonal antibodies directed at gp41 or the C-terminal gp120 epitopes, and no differences in binding to CD4 were noted.

Structure-function relationships of the HIV-1 envelope V3 loop tropism determinant: evidence for two distinct conformations

OBJECTIVE

The V3 loop of the HIV-1 envelope glycoprotein gp120 is an important determinant of HIV-1-specific cell tropism. Nine different purified envelope proteins were prepared in order to examine the association between the structure of the gp120 proteins and functional properties of HIV-1 virions differing in their tropism for T-cell lines and macrophages.

RESULTS

Six monoclonal antibodies to the V3 loop reacted preferentially with T-cell line-tropic gp120 envelope proteins, and one monoclonal antibody reacted preferentially with macrophage-tropic gp120 envelope proteins. T-cell line-tropic gp120 envelope proteins were at least 10-fold more susceptible to V3 loop proteolytic cleavage by human thrombin, and 1000-fold more susceptible to V3 loop proteolytic cleavage by human mast cell tryptase than macrophage-tropic gp120 envelope proteins.

CONCLUSIONS

These findings suggest that there are two distinct conformations for the V3 loop of T-cell line-tropic and macrophage-tropic gp120 envelope proteins.

Dual regulation of silent and productive infection in monocytes by distinct human immunodeficiency virus type 1 determinants

The regulation of human immunodeficiency virus type 1 infection and replication in primary monocytes was investigated by mutagenesis of recombinant proviral clones containing an env determinant required for the infectivity of monocytes. Virus replication was assayed by determination of reverse transcriptase activity in culture fluids and by recovery of virus from monocytes following cocultivation with uninfected peripheral blood mononuclear cells. Three virus replication phenotypes were observed in monocytes: productive infection, silent infection, and no infection. Incorporation of the monocytetropic env determinant in a full-length clone incapable of infection or replication in primary monocytes (no infection) conferred the capacity for highly efficient virus replication in monocytes (productive infection). Clones with the env determinant but lacking either functional vpr or vpu genes generated lower replication levels in monocytes. Mutation of both vpr and vpu, however, resulted in nearly complete attenuation of virus replication in monocytes, despite subsequent virus recovery from infected monocytes by cocultivation with uninfected peripheral blood mononuclear cells (silent infection). These findings indicate a central role for the "accessory" genes vpu and vpr in productive human immunodeficiency virus type 1 replication in monocytes and indicate that vpu and vpr may be capable of functional complementation.

Macrophage tropism determinants of human immunodeficiency virus type 1 in vivo

Strains of human immunodeficiency virus type 1 differ in their abilities to infect and replicate in primary human macrophages. Chimeric clones were constructed from a provirus unable to infect macrophages (NLHX) and envelope sequences (V3 loop) of viruses derived without cultivation from brain (YU2 and w1-1c1) or spleen (w2-1b4) tissues. The substituted V3 loop sequences in each case were sufficient to confer upon NLHX the ability to infect macrophages. Furthermore, an envelope domain immediately N terminal to the V3 loop also was found to modulate the level of replication in macrophages. These results demonstrate that an envelope determinant derived directly from patients with AIDS confers HIV-1 tropism for macrophages.

Identification of a determinant within the human immunodeficiency virus 1 surface envelope glycoprotein critical for productive infection of primary monocytes

Profound differences exist in the replicative capacities of various human immunodeficiency virus 1 isolates in primary human monocytes. To investigate the molecular basis for these differences, recombinant full-length clones were constructed by reciprocal DNA fragment exchange between a molecular clone derived from a monocyte-tropic isolate (ADA) and portions of two full-length clones incapable of infection or replication in primary monocyte cultures (HXB2 and NL4-3). Virions derived from proviral clones that contained ADA sequences encoding vpu and the N and C termini of the surface envelope glycoprotein (gp120) were incapable of replication in monocytes. However, a 283-base-pair ADA sequence encoding amino acids 240-333 of the mature gp120 protein conferred the capacity for high-level virus replication in primary monocytes. The predicted amino acid sequence of this ADA clone differed from NL4-3 and HXB2 at 22 of 94 residues in this portion of gp120, which includes the entire third variable domain. Only 2 of 11 residues implicated in CD4 binding are located in this region of gp120 and are identical in HXB2, NL4-3, and ADA. Alignment of the ADA sequence with published amino acid sequences of three additional monocyte-replicative and three monocyte-nonreplicative clones indicates 6 discrete residues with potential involvement in conferring productive human immunodeficiency virus 1 infection of primary monocytes.

Formation of noninfectious HIV-1 virus particles lacking a full-length envelope protein

Deletions were constructed within a functional human immunodeficiency virus type 1 (HIV-1) proviral clone in order to assess the role of the envelope protein in virus particle formation. A graded exonuclease deletion technique was used to produce 12 clones with deletions of 175-308 nucleotides in the first conserved domain of envelope. This included 9 clones with frameshift deletions and 3 clones with in-frame deletions. Isogenic pairs of env deletion clones were produced with or without an additional deletion in the vif and vpr genes. Upon transfection, all clones produced virus particles, as determined by p24 antigen, reverse transcriptase, and sucrose gradient assays with conditioned media. Virus particles produced from clones with deletions in env or vif and vpr, or both regions, banded on sucrose gradients with a mobility similar to that of virus produced by the parental clone. The p24 gag capsid protein in the particles was resistant to trypsin, but the particles were disrupted by treatment with Triton X-100, suggesting the presence of a surrounding lipid bilayer. Furthermore, electron microscopic studies revealed both mature and immature virus particles derived from COS cells transfected with the env deletion clones. Cocultivation experiments with lymphoid cells and cells transfected with each of the env deletion clones demonstrated that the virus particles were noninfectious.

Limited sequence heterogeneity among biologically distinct human immunodeficiency virus type 1 isolates from individuals involved in a clustered infectious outbreak

Human immunodeficiency virus type 1 isolates were obtained over a 3-year period from blood, brain, and lung of three patients in a clustered infectious outbreak. This included a blood donor who was initially asymptomatic but subsequently developed AIDS-related complex and two neonatal transfusion recipients who developed AIDS. Isolates from brain and lung replicated to greater than 30-fold higher levels in primary monocyte cultures than did those from blood; no growth differences on primary lymphocytes were observed. Thirteen clones were obtained from seven isolates, and env sequences were determined. The predicted amino acid sequences among these clones differed by only 0.01% but differed by 15-27% when compared to previously sequenced isolates from other patients. The level of envelope amino acid sequence divergence noted among these isolates is considerably lower than that previously reported for other human immunodeficiency virus isolates. No differences in the envelope unique to lung or brain isolates compared to blood isolates were noted. This study provides evidence that mutations in the envelope may not be necessary for disease progression and that other portions of the viral genome may contribute to cell-specific tropism.