COVA1-18 neutralizing antibody protects against SARS-CoV-2 in three preclinical models

One year into the Coronavirus Disease 2019 (COVID-19) pandemic caused by Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2), effective treatments are still needed 1-3 . Monoclonal antibodies, given alone or as part of a therapeutic cocktail, have shown promising results in patients, raising the hope that they could play an important role in preventing clinical deterioration in severely ill or in exposed, high risk individuals 4-6 . Here, we evaluated the prophylactic and therapeutic effect of COVA1-18 in vivo , a neutralizing antibody isolated from a convalescent patient 7 and highly potent against the B.1.1.7. isolate 8,9 . In both prophylactic and therapeutic settings, SARS-CoV-2 remained undetectable in the lungs of COVA1-18 treated hACE2 mice. Therapeutic treatment also caused a dramatic reduction in viral loads in the lungs of Syrian hamsters. When administered at 10 mg kg - 1 one day prior to a high dose SARS-CoV-2 challenge in cynomolgus macaques, COVA1-18 had a very strong antiviral activity in the upper respiratory compartments with an estimated reduction in viral infectivity of more than 95%, and prevented lymphopenia and extensive lung lesions. Modelling and experimental findings demonstrate that COVA1-18 has a strong antiviral activity in three different preclinical models and could be a valuable candidate for further clinical evaluation.

Herpesvirus saimiri transformation of HIV type 1 suppressive CD8+ lymphocytes from an HIV type 1-infected asymptomatic individual

CD8+ T lymphocytes from HIV+ individuals can potently suppress HIV-1 replication in a noncytolytic manner. This suppression appears to be multifactorial and the molecules contributing have not been fully elucidated. As an approach to this question we used herpesvirus saimiri (HVS) to transform CD8+ T lymphocytes from an HIV+ asymptomatic donor to a continuously growing, activation-independent, IL-2-dependent phenotype. The transformed cell population, termed CD8(HVS), had an activated phenotype, contained HVS sequences, did not shed infectious HVS virus, and was polyclonal. The CD8(HVS) cells, despite the absence of detectable CTL activity, potently suppressed HIV-1 production by both autologous and heterologous CD4+ cells from infected donors. The CD8(HVS) cells in coculture also suppressed virus production from PBMCs acutely infected with syncytium-inducing (SI) strains or NSI primary isolates of HIV-1. The supernatants from the CD8(HVS) cells and their concentrates derived from these supernatants were suppressive to NSI primary isolates of HIV-1 but not to SI strains. Fractionation of these concentrates showed that the suppressive activity was associated with low molecular mass (6500- to 19,300-Da) protein species. Western blotting and ELISA indicated that the CC chemokines MIP-1alpha, MIP-1beta, and RANTES were present in these fractions. Antibody-blocking studies with antibodies to the CC chemokines indicated that a significant portion of the soluble HIV-suppressive activity was due to these molecules. However, these experiments also suggested the inhibitory activity of the CD8(HVS) cells in coculture is not due exclusively to the CC chemokines. The HVS-transformed cells provide a useful tool for the study of noncytolytic CD8+ T lymphocyte-mediated suppression of HIV-1.

Random copolymers containing specific ratios of negatively charged and aromatic amino acids bind V3 disulfide loop and neutralize diverse HIV type 1 isolates

Random copolymers of polyamino acids containing negatively charged and aromatic residues at specific ratios appear to bind HIV type 1 V3 loop and neutralize diverse laboratory isolates. At least the putative heparin binding domain and isoleucine residues in the amino half of V3 are involved in the interactions with these polymers. There are a number of interesting features common between these polymer's modes of binding to the V3 and the protease inhibition drug ABT-538.

Propensity for a leucine zipper-like domain of human immunodeficiency virus type 1 gp41 to form oligomers correlates with a role in virus-induced fusion rather than assembly of the glycoprotein complex

For a number of viruses, oligomerization is a critical component of envelope processing and surface expression. Previously, we reported that a synthetic peptide (DP-107) corresponding to the putative leucine zipper region (aa 553-590) of the transmembrane protein (gp41) of human immunodeficiency virus type 1 (HIV-1) exhibited alpha-helical secondary structure and self-associated as a coiled coil. In view of the tendency of this type of structure to mediate protein association, we speculated that this region of gp41 might play a role in HIV-1 envelope oligomerization. However, later it was shown that mutations which should disrupt the structural elements of this region of gp41 did not affect envelope processing, transport, or surface expression (assembly oligomerization). In this report we compare the effects of amino acid substitutions within this coiled-coil region on structure and function of both viral envelope proteins and the corresponding synthetic peptides. Our results establish a correlation between the destabilizing effects of amino acid substitutions on coiled-coil structure in the peptide model and phenotype of virus entry. These biological and physical biochemical studies do not support a role for the coiled-coil structure in mediating the assembly oligomerization of HIV-1 envelope but do imply that this region of gp41 plays a key role in the sequence of events associated with viral entry. We propose a functional role for the coiled-coil domain of HIV-1 gp41.

Induction of HIVMN neutralizing antibodies in primates using a prime-boost regimen of hybrid synthetic gp120 envelope peptides

We have tested synthetic peptides composed of Th (T1) and V3 loop B cell neutralizing determinants [SP10 MN(A)] of HIVMN gp120 and the fusogenic (F) domain of gp41 as immunogens in rhesus monkeys. After two immunizations with either HIV env peptide T1-SP10 MN(A) or F-T1-SP10 MN(A), rhesus monkey serum neutralization titers against the HIVMN isolate ranged from 1:160 to 1:1400, and in cell-cell syncytium inhibition assay ranged from 1:20 to 1:80. However, in contrast to animals immunized with T1-SP10 MN(A), animals immunized twice with F-T1-SP10 MN(A) had no rise in anti-gp120 and neutralizing antibodies with an additional immunization with F-T1-SP10 MN(A) peptide. One of 4 rhesus monkeys (18987) had anti-HIVMN antibodies that cross-neutralized divergent HIV isolates HIVIIIB and HIVRF. Serum from animal 18987 neutralized 5 of 10 HIV isolates tested, and neutralizing activity against HIVIIIB of 18987 serum was absorbed with the conserved gp120 loop V3 sequence IGPGRAF. Anti-HIV neutralizing antibodies were boosted after a 6-mo rest by 500 micrograms of T1-SP10 MN(A) in 4 of 4 animals previously immunized with T1-SP10 MN(A) and in 2 of 2 animals previously immunized with F-T1-SP10 MN(A). However, immunization after 6-mo rest of animal 18987 with 500 micrograms of T1-SP10 MN(A) peptide, although boosting anti-HIVMN neutralizing antibodies, selectively did not boost cross-neutralizing anti-HIVIIIB antibodies. Thus, synthetic peptides containing T and B cell epitopes of HIV gp120 can induce high levels of anti-HIVMN neutralizing antibodies in primates.

Induction of HIVMN neutralizing antibodies in primates using a prime-boost regimen of hybrid synthetic gp120 envelope peptides

We have tested synthetic peptides composed of Th (T1) and V3 loop B cell neutralizing determinants [SP10 MN(A)] of HIVMN gp120 and the fusogenic (F) domain of gp41 as immunogens in rhesus monkeys. After two immunizations with either HIV env peptide T1-SP10 MN(A) or F-T1-SP10 MN(A), rhesus monkey serum neutralization titers against the HIVMN isolate ranged from 1:160 to 1:1400, and in cell-cell syncytium inhibition assay ranged from 1:20 to 1:80. However, in contrast to animals immunized with T1-SP10 MN(A), animals immunized twice with F-T1-SP10 MN(A) had no rise in anti-gp120 and neutralizing antibodies with an additional immunization with F-T1-SP10 MN(A) peptide. One of 4 rhesus monkeys (18987) had anti-HIVMN antibodies that cross-neutralized divergent HIV isolates HIVIIIB and HIVRF. Serum from animal 18987 neutralized 5 of 10 HIV isolates tested, and neutralizing activity against HIVIIIB of 18987 serum was absorbed with the conserved gp120 loop V3 sequence IGPGRAF. Anti-HIV neutralizing antibodies were boosted after a 6-mo rest by 500 micrograms of T1-SP10 MN(A) in 4 of 4 animals previously immunized with T1-SP10 MN(A) and in 2 of 2 animals previously immunized with F-T1-SP10 MN(A). However, immunization after 6-mo rest of animal 18987 with 500 micrograms of T1-SP10 MN(A) peptide, although boosting anti-HIVMN neutralizing antibodies, selectively did not boost cross-neutralizing anti-HIVIIIB antibodies. Thus, synthetic peptides containing T and B cell epitopes of HIV gp120 can induce high levels of anti-HIVMN neutralizing antibodies in primates.

Conversion of an immunogenic human immunodeficiency virus (HIV) envelope synthetic peptide to a tolerogen in chimpanzees by the fusogenic domain of HIV gp41 envelope protein

The fusogenic (F) domain of human immunodeficiency virus (HIV) gp41 envelope (env) protein has sequence similarities to many virus and mediates the fusion of HIV-infected cells. During a survey of the immunogenicity of HIV env peptides in chimpanzees, we have observed that HIV peptide immunogenicity was dramatically altered by the NH2-terminal synthesis of the gp41 F domain to an otherwise immunogenic peptide. We compared two hybrid peptide types comprised of T helper (Th) and B cell epitopes of HIV gp120 env protein for their immunogenicity in chimpanzees. The Th-B epitope hybrid peptides contained the HIV gp120 Th cell determinant, T1 (amino acids [aa] 428-440)-synthesized NH2 terminal to gp120 V3 loop peptides, which contain B cell epitopes that induce anti-HIV-neutralizing antibodies (SP10IIIB [aa 303-321] and SP10IIIB [A] [aa 303-327]). The F-Th-B peptide contained the HIV gp41 F domain of HIVIIIB gp41 (aa 519-530)-synthesized NH2 terminal to the Th-B peptide. Whereas Th-B peptides were potent immunogens for chimpanzee antibody and T cell-proliferative responses, the F-Th-B peptide induced lower anti-HIV gp120 T and B cell responses. Moreover, immunization of chimpanzees with F-Th-B peptide but not Th-B peptides induced a significant decrease in peripheral blood T lymphocytes (mean decrease during immunization, 52%; p < 0.02). Chimpanzees previously immunized with F-Th-B peptide did not respond well to immunization with Th-B peptide with T or B cell responses to HIV peptides, demonstrating that the F-Th-B peptide induced immune hyporesponsiveness to Th and B HIV gp120 env determinants. These observations raise the hypothesis that the HIV gp41 env F domain may be a biologically active immunoregulatory peptide in vivo, and by an as yet uncharacterized mechanism, promotes primate immune system hyporesponsiveness to otherwise immunogenic peptides.

A synthetic peptide inhibitor of human immunodeficiency virus replication: correlation between solution structure and viral inhibition

A peptide designated DP-107 was synthesized containing amino acid residues 558-595 of the envelope glycoprotein gp160 of human immunodeficiency virus type 1 strain LAI (HIV-1LAI). Algorithms for secondary structure have predicted that this region of the envelope transmembrane protein should form an extended alpha-helix. Consistent with this prediction, analysis by circular dichroism (CD) indicated that, under physiological conditions, DP-107 is approximately 85% helical. The high degree of stable secondary structure in a synthetic peptide of this size suggests self-association typical of a coiled coil or leucine zipper. In biological assays, the peptide efficiently blocked virus-mediated cell-cell fusion processes as well as infection of peripheral blood mononuclear cells by both prototypic and primary isolates of HIV-1. A single amino acid substitution in the peptide greatly destabilized its solution structure as measured by CD and abrogated its antiviral activity. An analogue containing a terminal cysteine was oxidized to form a dimer, and this modification lowered the dose required for antiviral effect from 5 to about 1 microgram/ml. These results suggest that both oligomerization and ordered structure are necessary for biological activity. They provide insights also into the role of this region in HIV infection and the potential for development of a new class of antiviral agents.

Alteration of HIV-1 infectivity and neutralization by a single amino acid replacement in the V3 loop domain

The V3 loop (residues 303-338) of the human immunodeficiency virus type 1 (HIV-1) gp120 envelope protein represents a principal neutralizing determinant for the virus. An HIV-1 proviral clone containing a mutation in the V3 loop was constructed in which the proline residue at position 313 was changed to an alanine (P313-A). This mutation alters the conserved GPGR sequence that is found in the V3 loop sequences of different HIV-1 isolates. The P313-A clone produced virus particles, which were infectious for a number of T-cell lines including MOLT-4, CEM, and SupT1, but demonstrated a relatively low infectivity on the AA5 B-cell line when compared with wild-type viruses, HTLV-IIIB, HXB2/10 (a chimeric molecular clone), and another mutant virus (Q290-T). V3 loop-specific neutralizing polyclonal sera and the 9284 monoclonal antibody, which recognizes the amino side of the V3 loop sequence, effectively blocked infectivity and syncytia formation of all viruses tested. In contrast, the 0.5 beta monoclonal antibody, which is biologically more potent than 9284 and recognizes a different V3 loop determinant, failed to neutralize the P313-A virus. These results suggest that the proline residue in the relatively conserved GPGR "turn" region of the V3 loop is crucial for recognition by the 0.5 beta antibody. The observed variation in sensitivity of the B-cell line to the P313-A virus may reflect the presence of cell-specific factors which could be important in establishing an HIV-1 infection.

Synthetic peptides containing T and B cell epitopes from human immunodeficiency virus envelope gp120 induce anti-HIV proliferative responses and high titers of neutralizing antibodies in rhesus monkeys

We have previously described a synthetic peptide (T1-SP10) derived from two noncontiguous regions of HTLVIIIB envelope gp120 (T1, amino acids 428-443; SP10, amino acids 303-321) that induced type-specific anti-HIV neutralizing antibodies and T cell proliferative responses against native HIV gp120 when used as a carrier-free immunogen in goats. In this study, HTLVIIIB T1-SP10 synthetic peptides were used to immunize rhesus monkeys to determine if the peptides were capable of eliciting HIV-specific neutralizing antibody and proliferative responses in primates. Four compounds (alum, polyA:polyU, threonyl-muramyldipeptide (MDP) and IFA) were also compared for efficacy as adjuvants in this system. Rhesus monkeys immunized with T1-SP10 peptides generated high titers of antibodies against the immunogens and also against HTLVIIIB gp120. Sera from all four animals given T1-SP10 in IFA or threonyl-MDP neutralized infection by HTLVIIIB and blocked virus-dependent cell fusion events. A peak neutralization titer of 1:940 was seen in one animal given IFA (19600) and a titer of 1:900 was seen in one of the monkeys (17371) given threonyl-MDP. Proliferative responses of immune rhesus PBMC to T1-SP10 appeared after the first injection. After eight immunizations, two of eight monkeys (one injected with peptides in threonyl-MDP and one given peptides in IFA) had PBMC proliferative responses to native HTLVIIIB gp120. These data demonstrate that the carrier-free T1-SP10 synthetic peptide construct can induce high titers of neutralizing anti-HIV antibody responses and PBMC proliferative responses to HIV in primates.

Synthetic peptides containing T and B cell epitopes from human immunodeficiency virus envelope gp120 induce anti-HIV proliferative responses and high titers of neutralizing antibodies in rhesus monkeys

We have previously described a synthetic peptide (T1-SP10) derived from two noncontiguous regions of HTLVIIIB envelope gp120 (T1, amino acids 428-443; SP10, amino acids 303-321) that induced type-specific anti-HIV neutralizing antibodies and T cell proliferative responses against native HIV gp120 when used as a carrier-free immunogen in goats. In this study, HTLVIIIB T1-SP10 synthetic peptides were used to immunize rhesus monkeys to determine if the peptides were capable of eliciting HIV-specific neutralizing antibody and proliferative responses in primates. Four compounds (alum, polyA:polyU, threonyl-muramyldipeptide (MDP) and IFA) were also compared for efficacy as adjuvants in this system. Rhesus monkeys immunized with T1-SP10 peptides generated high titers of antibodies against the immunogens and also against HTLVIIIB gp120. Sera from all four animals given T1-SP10 in IFA or threonyl-MDP neutralized infection by HTLVIIIB and blocked virus-dependent cell fusion events. A peak neutralization titer of 1:940 was seen in one animal given IFA (19600) and a titer of 1:900 was seen in one of the monkeys (17371) given threonyl-MDP. Proliferative responses of immune rhesus PBMC to T1-SP10 appeared after the first injection. After eight immunizations, two of eight monkeys (one injected with peptides in threonyl-MDP and one given peptides in IFA) had PBMC proliferative responses to native HTLVIIIB gp120. These data demonstrate that the carrier-free T1-SP10 synthetic peptide construct can induce high titers of neutralizing anti-HIV antibody responses and PBMC proliferative responses to HIV in primates.

Antibody raised against soluble CD4-rgp120 complex recognizes the CD4 moiety and blocks membrane fusion without inhibiting CD4-gp120 binding

We studied the humoral response of mice immunized with soluble CD4-rgp120 complex, testing polyclonal and monoclonal antibodies (mAbs) with the aim of identifying molecular changes that take place after the first interaction between human immunodeficiency virus and the cell surface. The antisera had a paradoxically high syncytia-blocking titer associated with anti-CD4 specificity, while their capacity to inhibit CD4-gp120 binding was relatively modest. One of the mAbs produced from these responders blocks syncytia formation but does not inhibit CD4 interaction with gp120. Apparently, this mAb interacts with the CD4 moiety of CD4-gp120 complex and prevents a post-binding event necessary for membrane fusion and viral infection.

Principal neutralizing domain of the human immunodeficiency virus type 1 envelope protein

The principal neutralizing determinant of human immunodeficiency virus type 1 (HIV-1) is located in the external envelope protein, gp120, and has previously been mapped to a 24-amino acid-long sequence (denoted RP135). We show here that deletion of this sequence renders the envelope unable to elicit neutralizing antibodies. In addition, using synthetic peptide fragments of RP135, we have mapped the neutralizing determinant to 8 amino acids and found that a peptide of this size elicits neutralizing antibodies. This sequence contains a central Gly-Pro-Gly that is generally conserved between different HIV-1 isolates and is flanked by amino acids that differ from isolate to isolate. Antibodies elicited by peptides from one isolate do not neutralize two different isolates, and a hybrid peptide, consisting of amino acid sequences from two isolates, elicits neutralizing antibodies to both isolates. By using a mixture of peptides of this domain or a mixture of such hybrid peptides the type-specificity of the neutralizing antibody response to this determinant can perhaps be overcome.

Antibodies that inhibit fusion of human immunodeficiency virus-infected cells bind a 24-amino acid sequence of the viral envelope, gp120

Antisera to recombinant human immunodeficiency virus (HIV) proteins containing the entire envelope, gp160, or the central portion of the envelope, PB1, can inhibit fusion of virally infected cells in culture. This fusion inhibition is HIV-variant specific--that is, anti-gp160-IIIB inhibits fusion of isolate HTLV-IIIB-infected cells but not of isolate HTLV-IIIRF-infected cells. Both anti-gp160 and anti-PB1 are completely blocked in fusion inhibition activity by the addition of PB1 protein. A 24-amino acid peptide (RP135, amino acids 307-330) completely blocks fusion inhibition activity of both antisera and also blocks the activity of serum from a chimpanzee infected with HTLV-IIIB. Thus, the principal epitope that elicits fusion-inhibiting antibodies is located in the central portion of gp120.