Anti-CD19 Chimeric Antigen Receptor T Cell Therapies: Harnessing the Power of the Immune System to Fight Diffuse Large B Cell Lymphoma

PURPOSE OF REVIEW

This article will review the use of anti-CD19 CAR-T therapy used in relapsed/refractory diffuse large B cell lymphoma.

RECENT FINDINGS

The clinical outcomes, safety analysis, and other relevant considerations will be discussed with an emphasis on the most recently published data regarding the ZUMA-1, JULIET, and TRANSCEND NHL-001 trials. Anti-CD19 CAR-T therapy is an exciting new therapy now approved and available to patients with relapsed/refractory diffuse large B cell lymphoma. Secondary to the increasing success and availability of these products, caregivers should expect to become familiar with the indications, toxicity, and limitations of these treatment options and when patients should be considered for referral.

Multicentre retrospective study of intravascular large B-cell lymphoma treated at academic institutions within the United States

Intravascular large B-cell lymphoma (IVLBCL) is a rare entity, with a generally aggressive course that may vary based on geographic presentation. While a United States (US) registry study showed relatively good outcomes with IVLBCL, clinicopathological and treatment data were unavailable. We performed a detailed retrospective review of cases identified at 8 US medical centres, to improve understanding of IVLBCL and inform management. We compiled data retrieved via an Institutional Review Board-approved review of IVLBCL cases identified from 1999 to 2015 at nine academic institutions across the US. We characterized the cohort's clinical status at time of diagnosis, presenting diagnostic and clinical features of the disease, treatment modalities used and overall prognostic data. Our cohort consisted of 54 patients with varying degrees of clinical features. Adjusting for age, better performance status at presentation was associated with increased survival time for the patients diagnosed in vivo (hazard ratio: 2·12, 95% confidence interval 1·28, 3·53). Based on the data we have collected, it would appear that the time interval to diagnosis is a significant contributor to outcomes of patients with IVLBCL.

How I manage ibrutinib intolerance and complications in patients with chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) therapy has changed dramatically with the introduction of several targeted therapeutics. Ibrutinib was the first approved for use in 2014 and now is used for initial and salvage therapy of CLL patients. With its widespread use in clinical practice, ibrutinib's common and uncommon adverse events reported less frequently in earlier clinical trials have been experienced more frequently in real-world practice. In particular, atrial fibrillation, bleeding, infections, and arthralgias have been reported. The management of ibrutinib's adverse events often cannot be generalized but must be individualized to the patient and their long-term risk of additional complications. When ibrutinib was initially developed, there were limited therapeutic alternatives for CLL, which often resulted in treating through the adverse events. At the present time, there are several effective alternative agents available, so transition to an alternative CLL directed therapy may be considered. Given the continued expansion of ibrutinib across many therapeutic areas, investigation of the pathogenesis of adverse events with this agent and also clinical trials examining therapeutic approaches for complications arising during therapy are needed. Herein, we provide strategies we use in real-world CLL clinical practice to address common adverse events associated with ibrutinib.

Drug-free macromolecular therapeutics induce apoptosis in cells isolated from patients with B cell malignancies with enhanced apoptosis induction by pretreatment with gemcitabine

Drug-free macromolecular therapeutics (DFMT) is a new paradigm for the treatment of B cell malignancies. Apoptosis is initiated by the biorecognition of complementary oligonucleotide motifs at the cell surface resulting in crosslinking of CD20 receptors. DMFT is composed from two nanoconjugates: 1) bispecific engager, Fab'-MORF1 (anti-CD20 Fab' fragment conjugated with morpholino oligonucleotide), and 2) a crosslinking (effector) component P-(MORF2)_X (N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer grafted with multiple copies of complementary morpholino oligonucleotide). We evaluated this concept in 44 samples isolated from patients diagnosed with various subtypes of B cell malignancies. Apoptosis was observed in 65.9% of the samples tested. Pretreatment of cells with gemcitabine (GEM) or polymer-gemcitabine conjugate (2P-GEM) enhanced CD20 expression levels thus increasing apoptosis induced by DFMT. These positive results demonstrated that DFMT has remarkable therapeutic potential in various subtypes of B cell malignancies.

A single-institution retrospective cohort study of first-line R-EPOCH chemoimmunotherapy for Richter syndrome demonstrating complex chronic lymphocytic leukaemia karyotype as an adverse prognostic factor

Richter Syndrome, an aggressive lymphoma occurring in patients with chronic lymphocytic leukaemia (CLL), has a generally poor prognosis and anthracycline-based chemoimmunotherapy regimens designed to treat de novo diffuse large B-cell lymphoma achieve modest clinical benefit. R-EPOCH (rituximab, etoposide, prednisone, vincristine, cyclophosphamide, doxorubicin) has demonstrated greater activity against aggressive B-cell histologies but has not been studied in Richter Syndrome. We conducted a retrospective cohort study of 46 Richter Syndrome patients treated with first-line R-EPOCH at our institution between 1 January 2006 and 31 May 2014. The median progression-free survival (PFS) was 3·5 months [95% confidence interval (CI): 2·0-7·6] and median overall survival (OS) was 5·9 months (95% CI: 3·2-10·3). Toxicity was high and 30% of patients died without progression or response. Patients with a complex CLL karyotype had significantly shorter PFS and OS (P = 0·005 and P = 0·002, respectively). Multivariable analysis identified complex CLL karyotype as the most significant predictor of decreased survival [Hazard ratio (HR) 2·72, 95% CI: 1·14-6·52, P = 0·025], adjusting for number of prior CLL treatments (P = 0·036). Richter Syndrome patients with complex CLL karyotype experience poor survival with R-EPOCH treatment and novel approaches are needed for these patients. In contrast, survival of patients without a complex CLL karyotype was similar to patients with de novo diffuse large B-cell lymphoma.

Outcomes of adults and children with primary mediastinal B-cell lymphoma treated with dose-adjusted EPOCH-R

Treatment with dose-adjusted EPOCH (etoposide, doxorubicin, cyclophosphamide, vincristine, prednisone) chemotherapy and rituximab (DA-EPOCH-R) has become the standard of care for primary mediastinal B-cell lymphoma (PMBCL) at many institutions despite limited data in the multi-centre setting. We report a large, multi-centre retrospective analysis of children and adults with PMBCL treated with DA-EPOCH-R to characterize outcomes and evaluate prognostic factors. We assessed 156 patients with PMBCL treated with DA-EPOCH-R across 24 academic centres, including 38 children and 118 adults. All patients received at least one cycle of DA-EPOCH-R. Radiation therapy was administered in 14·9% of patients. With median follow-up of 22·6 months, the estimated 3-year event-free survival (EFS) was 85·9% [95% confidence interval (CI) 80·3-91·5] and overall survival was 95·4% (95% CI 91·8-99·0). Outcomes were not statistically different between paediatric and adult patients. Thrombotic complications were reported in 28·2% of patients and were more common in paediatric patients (45·9% vs. 22·9%, P = 0·011). Seventy-five per cent of patients had a negative fluorodeoxyglucose positron emission tomography (FDG-PET) scan at the completion of DA-EPOCH-R, defined as Deauville score 1-3. Negative FDG-PET at end-of-therapy was associated with improved EFS (95·4% vs. 54·9%, P < 0·001). Our data support the use of DA-EPOCH-R for the treatment of PMBCL in children and adults. Patients with a positive end-of-therapy FDG-PET scan have an inferior outcome.

Continued Risk of Relapse Independent of Treatment Modality in Limited-Stage Diffuse Large B-Cell Lymphoma: Final and Long-Term Analysis of Southwest Oncology Group Study S8736

PURPOSE

Utility of combined-modality therapy for patients with limited-stage diffuse large B-cell lymphoma (DLBCL) was shown in the Southwest Oncology Group (SWOG) S8736 study, where three cycles of CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) plus radiotherapy (CHOP3RT) improved 5-year progression-free (PFS) and overall survival (OS) compared with eight cycles of CHOP (CHOP8). Subsequent analysis showed an unexpected overlap of the PFS curves. We aimed to confirm and investigate this observation by performing long-term analysis of SWOG S8736 and evaluating these data alongside data from similar patients receiving rituximab and CHOP3RT (SWOG S0014 study).

PATIENTS AND METHODS

A subset of patients with limited-stage DLBCL randomly assigned to CHOP8 (n = 150) or CHOP3RT (n = 158) in S8736 was analyzed along with a 56-patient subset treated in S0014 for long-term PFS and OS.

RESULTS

Median follow-up in S8736 was 17.7 years. In patients receiving CHOP8 and CHOP3RT, median PFS was 12.0 (95% CI, 8.8 to 14.3) and 11.1 years (95% CI, 8.9 to 14.4), respectively. There were no statistically significant differences in PFS between the groups (P = .73). Median OS was 13.0 (95% CI, 10.4 to 15.2) and 13.7 years (95% CI, 11.1 to 19.4) for patients treated with CHOP8 and CHOP3RT, respectively. Similarly, there were no statistically significant differences in OS between the groups (P = .38). With a median follow-up time 12 years in S0014, 5- and 10-year OS were 82% and 67%, respectively, with a persistent pattern of relapse despite the addition of rituximab.

CONCLUSION

Although 5-year PFS and OS were improved after early analysis in patients with limited-stage DLBCL receiving CHOP3RT versus CHOP8, extended survival data showed similar PFS and OS, with continuous treatment failure. The addition of rituximab (S0014) to combined-modality therapy did not mitigate the continued relapse risk, underscoring the value of prolonged clinical trial patient observation and possible unique biology of limited-stage DLBCL.

Acalabrutinib (ACP-196) in Relapsed Chronic Lymphocytic Leukemia

BACKGROUND

Irreversible inhibition of Bruton's tyrosine kinase (BTK) by ibrutinib represents an important therapeutic advance for the treatment of chronic lymphocytic leukemia (CLL). However, ibrutinib also irreversibly inhibits alternative kinase targets, which potentially compromises its therapeutic index. Acalabrutinib (ACP-196) is a more selective, irreversible BTK inhibitor that is specifically designed to improve on the safety and efficacy of first-generation BTK inhibitors.

METHODS

In this uncontrolled, phase 1-2, multicenter study, we administered oral acalabrutinib to 61 patients who had relapsed CLL to assess the safety, efficacy, pharmacokinetics, and pharmacodynamics of acalabrutinib. Patients were treated with acalabrutinib at a dose of 100 to 400 mg once daily in the dose-escalation (phase 1) portion of the study and 100 mg twice daily in the expansion (phase 2) portion.

RESULTS

The median age of the patients was 62 years, and patients had received a median of three previous therapies for CLL; 31% had chromosome 17p13.1 deletion, and 75% had unmutated immunoglobulin heavy-chain variable genes. No dose-limiting toxic effects occurred during the dose-escalation portion of the study. The most common adverse events observed were headache (in 43% of the patients), diarrhea (in 39%), and increased weight (in 26%). Most adverse events were of grade 1 or 2. At a median follow-up of 14.3 months, the overall response rate was 95%, including 85% with a partial response and 10% with a partial response with lymphocytosis; the remaining 5% of patients had stable disease. Among patients with chromosome 17p13.1 deletion, the overall response rate was 100%. No cases of Richter's transformation (CLL that has evolved into large-cell lymphoma) and only one case of CLL progression have occurred.

CONCLUSIONS

In this study, the selective BTK inhibitor acalabrutinib had promising safety and efficacy profiles in patients with relapsed CLL, including those with chromosome 17p13.1 deletion. (Funded by the Acerta Pharma and others; ClinicalTrials.gov number, NCT02029443.).

Externally validated predictive clinical model for untreated del(17p13.1) chronic lymphocytic leukemia patients

Little is known about outcomes of patients with chronic lymphocytic leukemia (CLL) with del(17p13.1) karyotype at diagnosis. We reviewed 114 de novo del(17p13.1) CLL patients seen at our institution. Using proportional hazards models to identify pretreatment clinical variables significantly associated with treatment-free survival (TFS) and overall survival (OS), we developed a simplified risk score for de novo del(17p13.1) CLL patients to predict TFS and OS based on these variables. These scores, particularly the very highest, can be utilized to identify high-risk patients for expedient enrollment on clinical trials. Our data support careful observation for low-risk patients, potentially preventing unnecessary use of aggressive therapies.

Ibrutinib in mantle cell lymphoma patients: glass half full? Evidence and opinion

Mantle cell lymphoma (MCL) is a rare subtype of non-Hodgkin's lymphoma typically marked by an aggressive clinical course and a predilection for relapse. The B-cell receptor (BCR) signaling survival pathway is chronically activated in MCL, contributing to its pathogenesis. Ibrutinib is an inhibitor of Bruton's tyrosine kinase, a vital component of this pathway. This article details the current clinical experience with ibrutinib in the treatment of patients with MCL, including completed and published clinical trials and reviews potential adverse events (AEs) and pitfalls associated with ibrutinib therapy. Although most AEs experienced by patients treated with ibrutinib are mild, some can be severe and treatment limiting and may be attributed to off-target effects. Ibrutinib is a very promising agent for patients with MCL with notable response rates. However, when used as a single agent, around one third of patients relapse in the first 2 years of treatment. Recently reported combination therapies have shown significant activity. Emerging data evaluating potential mechanisms of drug resistance and the poor clinical outcomes after treatment failure are also discussed. Further understanding of resistance and its implications not only in relapsed disease but in the frontline setting are needed. Investigation of strategies to overcome resistance remains an area of high unmet clinical need. Evaluation of the impact of shorter treatment duration, effects on minimal residual disease, and incorporation of novel combinations are also warranted.

Ocaratuzumab, an Fc-engineered antibody demonstrates enhanced antibody-dependent cell-mediated cytotoxicity in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is common in both developed and developing nations where the need for inexpensive and convenient administration of therapy is apparent. Ocaratuzumab is a novel Fc-engineered humanized IgG1 anti-CD20 monoclonal antibody (mAb) designed for effective antibody-dependent cell-mediated cytotoxicity (ADCC) at very low concentrations that may facilitate sub-cutaneous (vs. intravenous) dosing. Here, we report ocaratuzumab's potency against CLL cells. In vitro assessment of ocaratuzumab's direct cytotoxicity (DC), complement-dependent cytotoxicity (CDC), antibody-dependent cellular phagocytosis (ADCP), and ADCC was performed on CLL cells. Ocaratuzumab induced DC, CDC, and ADCP similarly to rituximab or ofatumumab (anti-CD20 mAbs). However, ocaratuzumab showed an advantage in NK cell-mediated ADCC over these antibodies. In allogeneic ADCC, [E:T (effector:target) ratios = 25:1, 12:1, 6:1], ocaratuzumab (10 µg/mL) improved ADCC by ~3-fold compared with rituximab or ofatumumab (P<0.001 all tested E:T ratios). Notably, the superiority of ocaratuzumab-induced ADCC was observed at low concentrations (0.1-10 ug/ml; P<0.03; allogeneic assays). In extended allogeneic ADCC E:T titration, ocaratuzumab (0.1 µg/mL) demonstrated 19.4% more cytotoxicity than rituximab (E:T = 0.38:1; P = 0.0066) and 21.5% more cytotoxicity than ofatumumab (E:T = 1.5:1; P = 0.0015). In autologous ADCC, ocaratuzumab (10 µg/mL) demonstrated ~1.5-fold increase in cytotoxicity compared with rituximab or ofatumumab at all E:T ratios tested (E:Ts = 25:1,12:1,6:1; all P<0.001). Obinutuzumab, a glyco-engineered anti-CD20 mAb, showed no improvement in ADCC activity compared with ocaratuzumab. The enhanced ADCC of ocaratuzumab suggests that it may be effective at low concentrations. If supported by clinical investigation, this feature could potentially allow for subcutaneous dosing at low doses that could expand the potential of administering chemoimmunotherapy in developing countries.

Cyclophosphamide, alvocidib (flavopiridol), and rituximab, a novel feasible chemoimmunotherapy regimen for patients with high-risk chronic lymphocytic leukemia

Alvocidib has demonstrated efficacy in high-risk chronic lymphocytic leukemia (CLL) patients. In this phase I study, we combined cyclophosphamide, alvocidib and rituximab (CAR) in a schema designed to mitigate tumor lysis syndrome (TLS) seen previously with alvocidib. Nine nucleoside analog-naïve, high-risk patients received escalating doses of CAR therapy. Dose limiting toxicity was not experienced. No instances of TLS were observed. Patient responses included three complete remissions and four partial remissions. CAR was tolerable and active in high-risk CLL patients without TLS toxicity. With continued monitoring of toxicities, a phase Ib/II study of this combination as frontline therapy is warranted.

Chronic lymphocytic leukemia with del(17p13.1): a distinct clinical subtype requiring novel treatment approaches

Chronic lymphocytic leukemia (CLL) is a very heterogeneous disease with significant variation in clinical presentation, time to disease progression, survival, and aggressiveness of clinical course. A subgroup of patients who have been repeatedly identified as having a poor response to therapy are those with del(17p13.1)--identified by either interphase cytogenetics or other comparable strategies. Although there has been much progress over the past few years in the development of new therapeutic targets for CLL patients, this subgroup has continued to lag behind others. Because of the poor response or significant therapy-related toxicity experienced by patients with del(17p13.1)--and the small number of these patients included in clinical trials--current guidelines are unable to provide suggestions for the care of newly diagnosed, symptomatic but untreated patients (as well as relapsed patients) in this subgroup on account of the modest amount of evidence. However, novel agents are on the horizon that appear to be significantly more effective in this patient population, and these will likely shape the standard of care for these patients in the future.

Flavopiridol treatment of patients aged 70 or older with refractory or relapsed chronic lymphocytic leukemia is a feasible and active therapeutic approach

Older chronic lymphocytic leukemia patients have poor outcomes with standard treatments and are underrepresented in clinical trials. We retrospectively reviewed outcomes of refractory chronic lymphocytic leukemia patients in two age categories (≥70 and <70 years) treated with single-agent flavopiridol, a drug active in genomically high-risk patients, during two trials. No significant difference between older and younger patients was observed in response rates (43 vs. 47%) or progression-free survival (median 8.7 vs. 9.9 months, P>0.80). Although overall survival was worse in older patients (median 2.1 vs. 2.4 years, P=0.02); when adjusted for other factors this difference was no longer significant (P≥0.10). With the exception of infections (older 29% vs. younger 62%) no significant association with toxicity was observed. These data demonstrate that flavopiridol administration to older chronic lymphocytic leukemia patients is feasible, tolerable, and may have similar efficacy to that in younger patients. Development of treatment approaches including flavopiridol should be considered for these older patients.

Antibodies raised to short synthetic peptides with sequences derived from HIV-1 SF2 gp120 can both neutralize and enhance HIV-1 SF13: a later variant isolated from the same host

HIV-1 SF13 emerged in a patient with immunity to HIV-1 SF2. This study determined the effect of antibodies raised to HIV-1 SF2 on the replication of the later variant. Antisera in rats were raised previously to a complete set of overlapping, synthetic 15mer peptides following the sequence of HIV-1 SF2 gp120. These sera have now been used in neutralization and enhancement assays against viruses derived from molecular clones of both variants. The sets of peptides inducing neutralizing antibodies to the two variants overlap. Antibodies to the third variable region of HIV-1 SF2 only neutralize the homologous virus whereas those to the second and fourth variable regions neutralize both variants. In contrast, the sets of major epitopes involved in enhancement do not overlap. Epitopes for both variants form two clusters when superimposed on the conformation of the conserved regions. To determine if antibodies with the potential to enhance or neutralize HIV-1 SF2 change over time in infected individuals sera from chimpanzees were used because no material was still available from the original patient. Antibodies to HIV-1 SF2 neutralizing epitopes and HIV-1 SF13 enhancing epitopes were present in the circulation of chimpanzees infected with HIV-1 SF2. Once antibodies to the neutralizing epitopes were induced they persisted whereas antibodies to the enhancing epitopes varied with time after infection. Conditions may therefore exist within individual hosts where not only neutralizing but also enhancing antibodies have the potential to contribute to the selection pressure operating on the circulating population of polymorphic variants.

An experimental chemically inactivated HIV-1 vaccine induces antibodies that neutralize homologous and heterologous viruses

We have developed a unique multiple step procedure to inactivate human immunodeficiency virus chemically with a very high safety margin while retaining antigenically active structural virion proteins, including gp120, in the final immunogen. The whole virus preparation (1-10 micrograms per dose) was highly immunogenic in a variety of small mammals and induced antibodies that recognized homologous and heterologous strains of HIV-1. Sera from immunized animals bound to peptides representing the entire sequence of the external glycoprotein gp120. Neutralizing antibodies active against the homologous immunizing strain and against heterologous HIV-1 strains were also elicited. Sera with virus neutralizing activity did not bind to MHC class I proteins derived from the human cell line used to grow the virus.

Antisera raised against the second variable region of the external envelope glycoprotein of human immunodeficiency virus type 1 cross-neutralize and show an increased neutralization index when they act together with antisera to the V3 neutralization epitope

Antibodies have been raised against a synthetic peptide (IRDKIQKENALFRNL) containing a neutralizing epitope within the second variable region of the human immunodeficiency virus type 1 (HIV-1) SF2 strain external envelope glycoprotein (gp120) and also against equivalent peptides of the HIV-1 LAI, RF and MN isolates. The resulting antisera cross-react with heterologous peptides but binding to heterologous recombinant gp120 is more restricted. Antisera to HIV-1 SF2, RF and MN are able to neutralize homologous virus. Some cross-neutralization is also observed, but a consensus peptide failed to induce neutralizing antibodies to any of the isolates studied. Antibodies to the V2 and V3 epitopes give a higher neutralization index when acting together than when the individual sera are used alone. Antibodies induced in natural infection bind to two sets of hexamers within the region encompassed by the 15-mer peptide, and the response to these can differ between infected individuals and within the same host over time.

Comparison of polymerase chain reaction tests and faecal culture for detecting Mycobacterium paratuberculosis in bovine faeces

A polymerase chain reaction (PCR) test for M. paratuberculosis was developed based on a 218 bp segment of a DNA insertion sequence, IS900, that is specific for this organism. The method involved two consecutive amplification reactions, with the second set of primers being nested inside the first set. The method reliably detected 50 organisms/g faeces. This PCR test was applied to 32 bovine faecal specimens containing high, moderate or low numbers of M. paratuberculosis organisms as determined by culture. The PCR test detected all specimens containing > or = 1600 colony forming units (cfu)/g faeces, six of ten specimens with 160-480 cfu/g faeces but only two of 13 specimens containing < or = 112 cfu/g faeces. The sensitivity of this test was better than that of a commercial PCR test which was carried out on the same faecal specimens.

DNA fingerprinting of Mycobacterium bovis strains by restriction fragment analysis and hybridization with insertion elements IS1081 and IS6110

Strains of Mycobacterium bovis, the causative organism of bovine tuberculosis, can be clearly distinguished from each other by restriction fragment analysis. This method of DNA fingerprinting has been used for many epidemiological studies in New Zealand, but the technique presents practical difficulties that hinder its widespread use. The insertion element IS6110 is being widely used as a DNA probe for distinguishing restriction fragment polymorphisms among strains of Mycobacterium tuberculosis. Both this element and another recently sequenced element, IS1081, are also present in M. bovis. We assessed the usefulness of these two elements for distinguishing between 160 strains of M. bovis. These strains, most of which were isolated in New Zealand, were selected to be representative of the 95 different types that were identified among 530 strains that were previously typed by restriction fragment analysis. Fifteen IS6110 types were identified, but more than half of the strains representing 46 restriction types had the same IS6110 type. Virtually all M. bovis strains as well as strains of M. tuberculosis and Mycobacterium africanum had the same IS1081 type. The results indicate that for M. bovis, IS1081 cannot be used to type strains, IS6110 can be used to distinguish strains into broad groups, but only restriction fragment analysis is sufficiently sensitive for detailed epidemiological studies. An investigation of the host range of IS1081 revealed that, apart from its presence in species of the tuberculosis complex, it is also present in a strain of Mycobacterium xenopi.

Antibodies are produced to the variable regions of the external envelope glycoprotein of human immunodeficiency virus type 1 in chimpanzees infected with the virus and baboons immunized with a candidate recombinant vaccine

Chimpanzees infected with human immunodeficiency virus type 1 produce antibodies against the variable regions of the external envelope glycoprotein gp120. All five variable regions contain an epitope which is recognized by at least one of five chimpanzee sera. Each of the sera recognized a different pattern of epitopes. It is suggested that this varying response contributes to the emergence of variant viruses in the host. In contrast with the variability of the chimpanzees' response to replicating virus, that of baboons to a candidate recombinant vaccine is more uniform. Baboons injected with recombinant gp120 produced high levels of antibodies to epitopes within both the variable and conserved regions which coincided with epitopes previously shown to induce neutralizing antibodies.

Identification of an insertion sequence, IS1081, in Mycobacterium bovis

An insertion sequence, IS1081, in the genome of Mycobacterium bovis has been identified and sequenced. It is 1324 bp long with 15 bp inverted repeat ends and contains a large ORF. There are six copies of IS1081 in the genome of M. bovis and the element is also present in Mycobacterium tuberculosis. IS1081 is not closely related to other DNA elements described in actinomycetes but its putative transposase bears some resemblance to that of IS256 from Staphylococcus aureus. IS1081 may be useful for genetic manipulations and for developing a diagnostic test for bovine tuberculosis based on the polymerase chain reaction.

Glycosylation governs the binding of antipeptide antibodies to regions of hypervariable amino acid sequence within recombinant gp120 of human immunodeficiency virus type 1

Antibodies raised to an overlapping series of peptides following the amino acid sequence of the external envelope glycoprotein (gp 120) of human immunodeficiency virus type 1 (HIV-1) recognize eight regions in recombinant gp 120 molecules. If the recombinant molecules are glycosylated, three of these regions show a reduced capacity to bind antibody. Of the other five regions, two are strain-specific and carbohydrate restricts antibody binding to their N-terminal flanks, and three can be recognized by antibodies in recombinant gp 120 from an unrelated strain of HIV-1. Antibodies in sera from HIV-1-infected patients bind at high levels to peptides from five regions of gp 120. Of these regions, two coincide with those recognized by antibodies raised to peptides. Four of the five epitopes recognized by the rat antipeptide sera whose ability to bind antibody is influenced most by glycosylation, and three of the five regions which induce high levels of antibodies in patients' sera, contain putative glycosylation sites which are variable between strains of HIV-1. Such sites flank the putative neutralization and CD4-binding regions of gp 120. It is suggested that changes in the number and position of carbohydrate moieties following mutation can alternately mask and reveal epitopes. Masking an epitope can render a virus resistant to neutralization, whereas virus which binds antibody without being neutralized is able to gain entry to cells bearing antibody and complement receptors. Changes in the glycosylation pattern of gp 120 may therefore contribute to the control of HIV-1 spread within its host.

The immunodominance of epitopes within the transmembrane protein (gp41) of human immunodeficiency virus type 1 may be determined by the host's previous exposure to similar epitopes on unrelated antigens

Six major epitopes have been recognized within the transmembrane gp41 molecule of human immunodeficiency virus type 1 (HIV-1). The immunodominant epitope is also recognized by antibodies in sera from laboratory personnel and is similar to a linear sequence of amino acids in the genome protein of two rhinovirus serotypes. The hypothesis is presented that immunodominance is produced by multiple priming of the host, following repeated infections with viruses unrelated to HIV-1, which share similar epitopes.