The purpose of this study is to test whether delayed boosting (an extra administration of a vaccine) with the IHV01 (FLSC) protein and A244/AHFG with or without ALFQ will cause the body to make higher amounts of antibodies or different types of antibodies after the vaccination.

The purpose of this study is to define the safety and immunogenicity of IHV01 and A244/AHFG with and without ALFQ at a full dose and at a fractional dose (one-fifth of a full dose) in a late boost setting for participants who had previously received a late boost of AIDSVAX®B/E with or without ALVAC in RV306. Safety will be assessed through the frequency of the overall and specific post-vaccination reactions. Blood, lymph nodes, sigmoid tissue, and mucosal specimens/secretions will be collected to assess humoral, cell-mediated, innate, and mucosal immune responses.

Healthy, HIV-uninfected participants, at a low risk for HIV infection, available for 12 months, who were randomized to receive active vaccine in RV306 and completed all vaccinations will be enrolled. A total of 120 participants will be enrolled across four vaccination groups. In each group, 25 participants will receive IHV01 and A244/AHFG at a full or fractional dose with or without ALFQ and 5 participants will receive placebo. Participants will receive 2 intramuscular (IM) injections into the quadriceps muscle at Day 0. The same quadriceps muscle will be used for both injections. Participants randomized to receive the vaccines will have one injection of IHV01 and one injection of A244/AHFG at a full or fractional dose with or without ALFQ, whereas participants randomized to receive placebo will get 2 separate injections of Normal Saline. All placebo injection volumes will match the vaccine injection volumes for the group in which a participant has been randomized. Participants will be followed-up for up to 12 months after enrollment. Mucosal secretion collections and endocervical cytobrush/swab procedures will be performed at Days 0, 14, 168, and 336 on consenting participants. Leukapheresis, sigmoid biopsy, and lymph node biopsy procedures will be performed only at Day 14 on consenting participants.

Inclusion Criteria:

• Healthy, HIV-uninfected male and female participants

• Prior RV306 recipients who were randomized to receive active vaccine with late boosting at month 12, 15, or 18 and who completed all vaccinations

• Have a Thai identity card

• Must be at low risk for HIV infection per investigator assessment

• Must be able to understand and complete the informed consent process

• Must be capable of reading Thai

• Must successfully complete a Test of Understanding prior to enrollment

• Must be in good general health without clinically significant medical history

• HIV-uninfected per diagnostic algorithm within 45 days of enrollment

• Laboratory screening analysis:

  1. Hemoglobin: Women ≥11.0 g/dL, Men ≥11.5 g/dL
  2. White cell count: 4,000 to 11,000 cells/mm3
  3. Platelets: 150,000 to 450,000/mm3
  4. ALT and AST ≤1.25 institutional upper limit of reference range
  5. Creatinine: ≤1.25 institutional upper limit of reference range
  6. Urinalysis blood and protein no greater than 1+ and negative glucose

• Female-Specific Criteria:

  1. Not currently pregnant or breastfeeding and not planning to become pregnant during the first 3 months after study vaccine/placebo injections
  2. Negative pregnancy test for women at screening, prior to vaccination (same day), and prior to any of the invasive procedures
  3. Be using an adequate birth control method for 45 days prior to receipt of vaccine/placebo and for at least 3 months after receipt of the vaccine/placebo. Adequate birth control is defined as follows: Contraceptive medications delivered orally, intramuscularly, vaginally, or implanted, underneath the skin, surgical methods (hysterectomy or bilateral tubal ligation), condoms, diaphragms, intrauterine device, or abstinence

• Male-Specific Criteria:

  1. Be using an adequate birth control method for at least 3 months after receipt of the vaccine/placebo. For non-vasectomized male participants with female partners of child-bearing potential this includes the use of condoms or abstinence and/or their partner's use of contraceptive medications delivered orally, intramuscularly, vaginally, or implanted, underneath the skin, surgical methods (hysterectomy or bilateral tubal ligation), diaphragms, or intrauterine device.

Exclusion Criteria:

• Asplenia: any condition resulting in the absence of a functional spleen

• Bleeding disorder diagnosed by a medical doctor (e.g., factor deficiency, coagulopathy, or platelet disorder requiring special precautions)

• History of allergic reaction, anaphylaxis, or other serious adverse reaction to vaccines or components of the vaccines

• Volunteer has received any of the following substances:

  1. Chronic use of therapies that may modify immune response, such as IV immune globulin and systemic corticosteroids (in doses of > 20 mg/day prednisone equivalent for periods exceeding 10 days) Note: The following exceptions are permitted and will not exclude study participation: use of corticosteroid nasal spray for rhinitis, topical corticosteroids for an acute uncomplicated dermatitis; or a short course (duration of 10 days or less, or a single injection) of corticosteroid for a non-chronic condition (based on investigator clinical judgment) at least 14 days prior to enrollment in this study
  2. Blood products within 120 days prior to HIV screening
  3. Immunoglobulins within 30 days prior to HIV screening
  4. Any licensed vaccine within 14 days prior to study vaccine administration in the present study
  5. Receipt of any investigational HIV vaccine other than RV306 products
  6. Investigational research agents or vaccine within 30 days prior to enrollment in the present study
  7. Receipt of a Coronavirus disease 2019 (COVID-19) vaccine that has been given Emergency Use Authorization (or those that become licensed) by the Thai FDA within 14 days prior to study vaccine administration in the present study Note: Volunteers receiving a COVID-19 vaccine that requires 2 doses will not be enrolled until 14 days after the second dose has been administered
  8. Anti-tuberculosis prophylaxis or therapy during the past 90 days prior to enrollment

• Active sexually transmitted infection confirmed by clinical exam and diagnostic test

• Any medical, psychiatric, social condition, occupational reason, or other responsibility that, in the judgment of the investigator, is a contradiction to protocol compliance or impairs a volunteer's ability to give informed consent

• Psychiatric condition that precludes compliance with the protocol; past or present psychoses; past or present bipolar disorder; disorder requiring lithium; or within 5 years prior to enrollment, a history of suicide ideation or attempt

• Study site employees who are involved in the protocol and/or may have direct access to study related area

Determination of a participants eligibility will be completed at screening. Final evaluation of eligibility will be based on the medical judgment of the principal investigator or designee based on his/her medical and research experience.