At the heart of the DNA/ALVAC/gp120/alum vaccine’s efficacy in the absence of neutralizing antibodies is a delicate balance of pro- and anti-inflammatory immune responses that effectively decreases the risk of SIV_mac251 acquisition in macaques. Vaccine efficacy is linked to antibodies recognizing the V2 helical conformation, DC-10 tolerogenic dendritic cells eliciting the clearance of apoptotic cells via efferocytosis, and CCR5 downregulation on vaccine-induced gut homing CD4⁺ cells. RAS activation is also linked to vaccine efficacy, which prompted the testing of IGF-1, a potent inducer of RAS activation with vaccination. We found that IGF-1 changed the hierarchy of V1/V2 epitope recognition and decreased both ADCC specific for helical V2 and efferocytosis. Remarkably, IGF-1 also reduced the expression of CCR5 on vaccine-induced CD4⁺ gut-homing T-cells, compensating for its negative effect on ADCC and efferocytosis and resulting in equivalent vaccine efficacy (71% with IGF-1 and 69% without).

HTLV-1 type-A rarely causes lung disease in humans, whereas HTLV-1 type-C is more frequently associated with respiratory failure and premature death. We investigated the genetic basis of HTLV-1C morbidity by constructing a chimeric HTLV-1A/C _oI-L encompassing the highly divergent type C orf-I. We demonstrate that systemic infectivity of HTLV-1A and HTLV-1A/C _oI-L is equivalent in macaques, but viral expression in lungs is significantly higher in HTLV-1A/C _oI-L infection. In addition, bronchoalveolar-lavage immune cell dynamics differs greatly with neutrophils and monocytes producing TNF-α in HTLV-1A/C _oI-L , but producing IL-10 in HTLV-1A infection. Animals infected with HTLV-1A/C _oI-L develops bronchiectasis at 10 months from infection, but at the same timepoint those infected with HTLV-1A do not. HTLV-1A/C _oI-L expressed a 16 kDa fusion protein (p16C) via a doubly spliced, Rex-orf-IC, mRNA able to shield T-cells from efferocytosis, a monocyte function that mitigates inflammation via clearance of apoptotic cells. The Rex-orf-IC mRNA is expressed as more frequent in the lung of HTLV-1A/C _oI-L than HTLV-1A infected animals. Since defective efferocytosis is associated with lung obstructive pathologies, the data raise the hypothesis that p16C may contribute to the lung morbidity observed in HTLV-1C infection.

The human T-cell leukemia type-1 (HTLV-1) retrovirus establishes chronic life-long infection in a fraction of infected individuals associated with severe pathological conditions. Although the mechanism driving disease development is not fully understood, current evidence indicates the essential functions of viral regulatory proteins. Among these, the p13 protein has previously been shown to localize to the inner mitochondrial membrane in T cells, altering mitochondrial biology and T-cell function. While CD4⁺ T cells are the primary cell target of HTLV-1 infection, genomic viral DNA has also been detected in monocytes, macrophages, and dendritic cells, which orchestrate innate and adaptive immunity and play a critical role in protecting against virus-induce diseases by establishing the appropriate balance of pro and anti-inflammatory responses. Given the central role of mitochondria in monocyte differentiation, we investigated the effect of p13 in monocytes/macrophages and found that by localizing to mitochondria, p13 affects mitochondrial respiration. Moreover, we demonstrate that p13 expression affects macrophage polarization to favor the recruitment of CD4⁺ T cells, the primary target of the virus, potentially facilitating the spread of viral infection and the development of disease.

The transient depletion of monocytes alone prior to exposure of macaques to HTLV-1 enhances both HTLV-1_WT (wild type) and HTLV-1_p12KO (Orf-1 knockout) infectivity, but seroconversion to either virus is not sustained over time, suggesting a progressive decrease in virus expression. These results raise the hypotheses that either HTLV-1 persistence depends on a monocyte reservoir or monocyte depletion provides a transient immune evasion benefit. To test these hypotheses, we simultaneously depleted NK cells, CD8⁺ T cells, and monocytes (triple depletion) prior to exposure to HTLV-1_WT or HTLV-1_p12KO. Remarkably, triple depletion resulted in exacerbation of infection by both viruses and complete rescue of HTLV-1_p12KO infectivity. Following triple depletion, we observed rapid and sustained seroconversion, high titers of antibodies against HTLV-1 p24Gag, and frequent detection of viral DNA in the blood and tissues of all animals when compared with depletion of only CD8⁺ and NK cells, or monocytes alone. The infection of macaques with HTLV-1_WT or HTLV-1_p12KO was associated with higher plasma levels of IL-10 after 21 weeks, while IL-6, IFN-γ, IL-18, and IL-1β were only elevated in animals infected with HTLV-1_WT. The repeat depletion of monocytes, NK, and CD8⁺ cells seven months following the first exposure to HTLV-1 did not further exacerbate viral replication. These results underscore the contribution of monocytes in orchestrating anti-viral immunity. Indeed, the absence of orf-1 expression was fully compensated by the simultaneous depletion of CD8⁺ T cells, NK cells, and monocytes, underlining the primary role of orf-1 in hijacking host immunity.

Simian or Human immunodeficiency virus (SIV or HIV) vaccines based on V1-deleted envelope virus-like particles, delivered by the DNA/ALVAC platforms, followed by the ΔV1gp120 boost formulated in Alum, protect 50% and 80% of macaques from mucosal infection with SIV_mac251 or Simian-Human immunodeficiency virus, respectively. Adding the Army Liposome Formulation + QS21 (ALFQ) adjuvant to the ΔV1gp120+Alum boost (ALFQA) may enhance protective immune responses. Here, we show that ALFQA protects 58% of female macaques from infection following eleven exposures to SIV_mac251, achieving 79% vaccine efficacy. The ALFQA vaccine regimen augments mucosal CD73⁺CD163⁺ M2-like macrophages and NKp44⁺ innate lymphoid cells (ILCs), while reducing NKG2A^-NKP44^- cells producing interferon-γ. Antibody-Dependent Cellular Cytotoxicity (ADCC) targeting helical V2, and mucosal tolerogenic dendritic cells-10 (DC-10) and envelope-specific interleukin-17⁺ NKp44⁺ ILCs, correlate with decreased risk of infection. Plasma proteome analysis links vaccine efficacy to lymphotoxin-α, mucosal DC-10, and chemokine (C-C motif) ligand-8, a chemokine produced mainly by M2-macrophages. These data support the role of pro-resolution immunity in protection afforded by the V1-deleted SIV and HIV immunogens. The Combined Long-term Efferocytosis and ADCC Responses (CLEAR) phase I HIV-vaccine trial is designed to test the safety and immunogenicity of the Alum and ALFQA adjuvants in combination with V1-deleted HIV immunogens in humans.

Exposure to Bacillus Calmette-Guérin (BCG) or Canarypox ALVAC/Alum vaccine elicits pro- or antiinflammatory innate responses, respectively. We tested whether prior exposure of macaques to these immunogens protected against SARS-CoV-2 replication in lungs and found more efficient replication control after the pro-inflammatory immunity elicited by BCG. The decreased virus level in lungs was linked to early infiltrates of classical monocytes producing IL-8 with systemic neutrophils, Th2 cells, and Ki67 ⁺ CD95 ⁺ CD4 ⁺ T cells producing CCR7. At the time of SARS-CoV-2 exposure, BCG-treated animals had higher frequencies of lung infiltrating neutrophils and higher CD14 ⁺ cells expressing efferocytosis marker MERTK, responses correlating with decreased SARS-CoV-2 replication in lung. At the same time point, plasma IL-18, TNF-α, TNFSF-10, and VEGFA levels were also higher in the BCG group and correlated with decreased virus replication. Finally, after SARS-CoV-2 exposure, decreased virus replication correlated with neutrophils producing IL-10 and CCR7 preferentially recruited to the lungs of BCG-vaccinated animals. These data point to the importance of the spatiotemporal distribution of functional monocytes and neutrophils in controlling SARS-CoV-2 levels and suggest a central role of monocyte efferocytosis in curbing replication.