Clinical Trial to Evaluate the Safety, Tolerability, and Immunogenicity of 16055 NFL Delta Gly4 Env Protein Trimer and Trimer 4571 Combined With 3M-052-AF + Alum Adjuvant and Ad4-Env145NFL Viral Particles as Heterologous Prime-boost Regimens in Adult Participants Without HIV.

Inclusion Criteria:

• Able and willing to complete the informed consent process, including an Assessmentof Understanding (AoU): Volunteer demonstrates an understanding of this study andcompletes a questionnaire prior to signing the informed consent form with verbaldemonstration of understanding of questionnaire items that were answeredincorrectly.

• 18 to 55 years old, inclusive, on day of enrollment.

• Available for clinic follow-up and willing to undergo study procedures through thelast clinic visit.

• Agrees not to enroll in another study of an investigational agent duringparticipation in the trial. If a potential participant is already enrolled inanother clinical trial, approvals from the other trial sponsor and the HVTN 313 PSRTare required prior to enrollment into HVTN 313

• In good general health according to the clinical judgment of the site investigator.

• Physical examination and laboratory results without clinically significant findingsthat would interfere with assessment of safety or reactogenicity in the clinicaljudgement of the site investigator.

• Assessed by clinical staff as having a low likelihood of acquiring HIV perguidelines, agrees to discuss their potential for HIV acquisition, agrees torisk-reduction counseling, and agrees to avoid behaviors associated with a higherlikelihood of acquiring HIV through the final study visit. Low likelihood mayinclude persons stably taking pre-exposure prophylaxis (PrEP) as prescribed.

• Hemoglobin (Hgb):

• ≥ 11.0 g/dL for volunteers who were assigned female sex at birth (AFAB)

• ≥ 13.0 g/dL for volunteers who were assigned male sex at birth (AMAB) and fortransgender men who have been on hormone therapy for more than 6 consecutivemonths

• ≥ 12.0 g/dL for transgender women who have been on hormone therapy for morethan 6 consecutive months

• For transgender volunteers who have been on hormone therapy for less than 6consecutive months, determine hemoglobin eligibility based on the sex assignedat birth.

• White blood cell (WBC) count = 2,500 to 12,000/mm³ (WBC over 12,000/mm³ is notexclusionary if further evaluation shows general good health and if PSRT approval isgranted).

• Platelets = 125,000 to 550,000/mm³.

• Alanine aminotransferase (ALT) within the institutional normal range.

• Serum creatinine ≤ 1.1 x upper limit of normal (ULN) based on the institutionalnormal range.

• Serum calcium level of > 8.5 mg/dL (if the participant consented to haveleukapheresis as a study procedure).

• Blood pressure (BP) in the range of 90 to < 140 mmHg systolic and 50 to < 90 mmHgdiastolic.

• Negative HIV test results by one of the following options: For US volunteers:

• US Food and Drug Administration (FDA)-approved enzyme immunoassay (EIA)

• Chemiluminescent microparticle immunoassay (CMIA)

• Two negative results on HIV rapid tests (one of which must be FDA-approvedCMIA)

• Negative for anti-Hepatitis C virus (HCV) Abs (anti-HCV) or negative HCV nucleicacid test (NAT) if anti-HCV Abs are detected.

• Negative for Hepatitis B surface antigen.

• For AFAB or intersex at birth volunteers who are capable of becoming pregnant (hereafter referred to as "persons of pregnancy potential"):

• Must agree to use effective means of birth control from at least 21 days priorto enrollment through 8 weeks after their last scheduled vaccination timepoint (see Appendix H).

• Must have a negative beta human chorionic gonadotropin (β-HCG) pregnancy test (urine or serum) on day of enrollment.

• AMAB or intersex at birth volunteers must agree to not seek pregnancy throughalternative methods, such as oocyte retrieval, artificial insemination, or in vitrofertilization from at least 21 days prior to enrollment through 8 weeks after theirlast scheduled vaccination timepoint.

• AMAB volunteers must agree to consistently practice abstinence or another method ofeffective birth control during sexual intercourse with persons of pregnancypotential and must not donate sperm at least 21 days prior to each Ad4-Env145NFLvaccination through 28 days following each Ad4-Env145NFL vaccination.

• Willing to follow precautions as provided by the study team for preventing thespread of adenovirus in the community.

Inclusion criteria for contacts of Ad4-Env145NFL vaccinees:

• Able and willing to complete the informed consent process, including an Assessmentof Understanding (AoU): Volunteer demonstrates an understanding of this study andcompletes a questionnaire prior to enrollment with verbal demonstration ofunderstanding of questionnaire items that were answered incorrectly.

• Meets criteria of a household contact or intimate contact.

• A household contact is someone who resides (ie, lives in the same house orapartment) with the potential vaccinee within the first 28 days following eachAd4-Env145NFL vaccination.

• An intimate contact is defined as someone who engages in mouth-to-mouthkissing, sexual intercourse, or oral sex with the study participant within thefirst 28 days following each Ad4-Env145NFL vaccination.

• Available for clinic follow-up and willing to participate in study proceduresthrough the last scheduled clinic visit for the observational cohort.

• Age ≥ 18 years old on the day of enrollment.

Exclusion Criteria:

• Volunteer who is breastfeeding or pregnant.

• Body mass index (BMI) ≥ 40. Enrollment of individuals with BMI ≥ 40, whom the siteinvestigator assesses are in good health, may be considered by PSRT on acase-by-case basis.

• Diabetes mellitus (DM). Type 2 DM controlled with diet alone (and confirmed byHgbA1c ≤ 8% within the last 6 months) or a history of isolated gestational diabetesare not exclusionary. Enrollment of individuals with Type 2 DM that is wellcontrolled on hypoglycemic agent(s) may be considered by the PSRT on a case-by-casebasis, provided that the HgbA1c is ≤ 8% within the last 6 months (sites may drawthese at screening).

• Previous or current recipient of an investigational HIV vaccine (previous placeborecipients are not excluded).

• Receipt of non-HIV experimental vaccine(s) received within the last 1 year.Exceptions include vaccines that have subsequently undergone licensure or EmergencyUse Authorization (EUA) by the FDA or World Health Organization (WHO) emergency uselisting (EUL).

• Congenital or acquired immunodeficiency, including systemic medication (includesoral, intramuscular, or intravenously administrated medications) use likely toimpair immune response to vaccine in the opinion of the site investigator, such assystemic glucocorticoid use equal to or greater than prednisone 10 mg/day within 3months prior to enrollment.

• Blood products or immunoglobulin within 16 weeks prior to enrollment; receipt ofimmunoglobulin within 16 weeks prior to enrollment requires PSRT approval.

• Receipt of any live, attenuated, replicating vaccine within 4 weeks prior toenrollment or planned administration within 4 weeks after enrollment. Note forACAM2000 vaccine for mpox (formerly known as Monkeypox): the vaccination scab mustno longer be present and at least 4 weeks is required prior to enrollment.

• Receipt or planned receipt of any killed/subunit/inactivated/non-replicating vaccinewithin 2 weeks prior to enrollment or planned administration within 2 weeks afterenrollment. This applies to Jynneos vaccine for mpox which is non- replicating.

• Initiation of antigen-based immunotherapy for allergies within the previous year (stable immunotherapy is not exclusionary); inclusion of participants who initiatedimmunotherapy within the previous year requires PSRT approval.

• Receipt of investigational research agents with a half-life of 7 or fewer dayswithin 4 weeks prior to enrollment. If a potential participant has receivedinvestigational agents with a half-life greater than 7 days (or unknown half-life)within the past year, PSRT approval is required for enrollment.

• History of serious reaction (e.g., hypersensitivity, anaphylaxis) to any relatedvaccine or component of the study-vaccine regimen.

• Hereditary angioedema, acquired angioedema, or idiopathic forms of angioedema.

• Idiopathic urticaria within the past year.

• Bleeding disorder diagnosed by a clinician which would make study procedures acontraindication.

• Seizure disorder; febrile seizures as a child or seizures secondary to alcoholwithdrawal more than 5 years ago are not exclusionary.

• Asplenia or functional asplenia.

• Active duty and reserve US military personnel.

• Any other chronic or clinically significant condition that, in the clinicaljudgement of the investigator, would jeopardize the safety or rights of the studyparticipant, including, but not limited to: clinically significant forms ofsubstance use disorder or alcohol use disorder, serious psychiatric disorders,persons with any suicide attempt within the past 1 year (if between 1 and 2 years,consult PSRT for approval), or cancer that, in the clinical judgement of the siteinvestigator, has a potential for recurrence (excluding basal cell carcinoma).

• Asthma is excluded if the participant has ANY of the following:

• Required either oral or parenteral corticosteroids for an exacerbation 2 ormore times within the past year, OR

• Needed emergency care, urgent care, hospitalization, or intubation for an acuteasthma exacerbation within the past year (eg, would NOT exclude individualswith asthma who meet all other criteria but sought urgent/emergent care solelyfor asthma medication refills or co-existing conditions unrelated to asthma);OR

• Uses a short-acting rescue inhaler more than 2 days/week for acute asthmasymptoms (i.e., not for preventive treatment prior to athletic activity); OR

• Uses medium-to-high-dose inhaled corticosteroids (greater than 250 mcgfluticasone or therapeutic equivalent per day), whether in single-therapy ordual-therapy inhalers (i.e., with a long-acting beta agonist, OR

• Uses more than 1 medication for maintenance therapy daily. Inclusion of anyoneon a stable dose of more than 1 medication for maintenance therapy daily forgreater than 2 years requires PSRT approval.

• A participant with a history of a potential immune-mediated medical condition (PIMMC), either active or remote. Specific examples are listed in Appendix I (AESIindex). Not exclusionary: mild psoriasis that does not require ongoing systemictreatment.

• Investigator concern for difficulty with venous access based upon clinical historyand physical examination. For example, persons with a history of intravenous druguse or substantial difficulty with previous blood draws.

• Individuals who expect to live in the same household with or provide care for any ofthe following, within 28 days following each of the third through fifth studyvaccination timepoints:

• An individual under 5 years of age

• An individual who is immunocompromised, immunosuppressed, or has any conditionwhich would place them at undue risk for complications of an adenoviralinfection, per the investigator's judgement

• A person who is currently pregnant or breastfeeding or planning a pregnancyduring the period of study vaccination

• Individuals who are unable or unwilling to avoid intimate contact for at least 28days following each Ad4-Env145NFL vaccination with individuals with any of thefollowing:

• Immunocompromised or immunosuppressed condition

• Are currently pregnant or breastfeeding or planning a pregnancy during theperiod of study vaccination

• Any condition which would place them at undue risk for complications of anadenoviral infection, per the investigator's judgement

• History of thrombosis with thrombocytopenia (TTS) or HIT with or without thrombosis.

• History of a medical condition, including use of intranasal steroids thatcompromises the integrity of the nasal/cerebrospinal fluid (CSF) barrier and posesundue risk for complications of the Ad4-Env145NFL IN vaccination, per investigatorjudgement.

• History of a surgical condition that compromises the integrity of thenasal/cerebrospinal fluid (CSF) barrier and poses undue risk for complications ofthe Ad4-Env145NFL IN vaccination, per investigator judgement.

Exclusion criteria for contacts of Ad4-Env145NFL vaccinees:

• Any condition that, in the investigator's judgment, places the participant at unduerisk by participating in the study.