Patients with autoimmune disease who are otherwise eligible must not have received steroid and immunosuppressive therapy within days prior to registration Has a diagnosis of immunodeficiency, is receiving systemic steroid therapy (except for physiological dose levels), or immunosuppressive therapies SAFETY RUN-IN: Diagnosis of immunosuppression or receiving steroid therapy or other immunosuppressive therapy within weeks of the study RANDOMIZED PHASE II CLINICAL TRIAL: Diagnosis of immunosuppression or receiving steroid therapy or other immunosuppressive therapy within weeks of the study Any systemic steroid therapy or other form of immunosuppressive therapy within days of the first dose of mRNA- or pembrolizumab Is receiving systemic steroid therapy ? days prior to the first dose of study therapy or receiving any other form of immunosuppressive medication Must not have a diagnosis of immunodeficiency, or receiving systemic steroid therapy, or any other form of immunosuppressive therapy within days prior to trial treatment; short burst of steroids of - days (for chronic obstructive pulmonary disease [COPD] exacerbation or other similar indication) are allowed Patients who are planned to receive concurrent growth factor, systemic steroid or other immunosuppressive therapy or cytotoxic agent Patients receiving systemic steroid therapy or any other systemic immunosuppressive medication. Local steroid therapies are acceptable Systemic steroid therapy or any immunosuppressive therapy Systemic steroid or other immunosuppressive therapy within weeks of starting the study Ongoing treatment with steroid therapy or other immunosuppressive Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of HiDAC treatment; NOTE: use of steroid eye drops starting at the time of HiDAC administration is allowed Receiving systemic steroid therapy or any other form of systemic immunosuppressive therapy =< days prior to registration; EXCEPTIONS:\r\n* Low doses of steroids (=< mg of prednisone or equivalent dose of other steroid/day)\r\n* Previous use of corticosteroids is allowed\r\n* After initiation of MK- therapy, steroid can be used for management of potential immune mediated adverse events (AE) for less than weeks of therapy\r\n* Topical, ocular, intra-articular, intranasal, and inhalational corticosteroids (with minimal systemic absorption) are permitted Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of trial treatment; physiologic doses of steroid therapy (? mg/day dexamethasone equivalents) by the time of first dose of treatment are allowed Systemic steroid therapy or any other form of immunosuppressive therapy within days prior to registration Receiving systemic steroid therapy or any form of immunosuppressive therapy within week prior to the start of study drug Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of trial treatment. The use of physiologic doses of corticosteroids may be approved after consultation with the Sponsor. Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of systemic immunosuppressive therapy within days prior to the first dose of trial treatment; topical, inhaled, ocular, and intra-articular steroids are not exclusionary Diagnosis of immunosuppression or receiving steroid therapy or other immunosuppressive therapy within weeks of the study Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of trial treatment\r\n* Short-term administration of systemic steroids (i.e., for allergic reactions or the management of immune related adverse events [irAEs]) is allowed Subjects must not be receiving systemic steroid therapy or any other form of immunosuppressive therapy within weeks prior to the first dose of study medication; the use of physiologic doses of corticosteroids is acceptable Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of trial treatment; the use of physiologic doses of corticosteroids may be approved after consultation with the sponsor Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of trial treatment; the use of physiologic doses of corticosteroids may be approved after consultation with the principal investigator (PI) and Merck Is receiving systemic steroid therapy within three days prior to the first dose of trial treatment or receiving any other form of immunosuppressive medication (corticosteroid use on study for management of early combined immunosuppression [ECIs] is allowed) Systemic steroid therapy unless for physiologic replacement Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of trial treatment; the use of physiologic doses of corticosteroids for adrenal and pituitary insufficiency is not considered a form of systemic steroid therapy and would not exclude a subject from the study Has a diagnosis of immunodeficiency or is receiving systemic immunosuppressive therapy within days of study entrance Has a known history of immunosuppression or is receiving systemic steroid therapy or any other form of systemic immunosuppressive therapy within days Systemic steroid therapy or immunosuppressive therapy within days before vaccine administration ADDITIONAL CRITERIA FOR STUDY CONTINUATION: Systemic steroid or immunosuppressive therapy within days before vaccine administration Systemic or topical steroid use or other immunosuppressive therapy within the past days Patient has a diagnosis of immunodeficiency or is receiving ongoing immunosuppressive therapy, including systemic or enteric corticosteroids except for non-systemically absorbed treatments (such as inhaled or topical steroid therapy for asthma, chronic obstructive pulmonary disease, allergic rhinitis). Patient must be off systemic steroid or any other form of immunosuppressive therapy within days prior to first dose of trial treatment History of organ transplant requiring immunosuppression; or history of pneumonitis or interstitial lung disease requiring treatment with systemic steroids; or a history of receiving systemic steroid therapy or any other immunosuppressive medication ? days prior to study initiation. Daily steroid replacement therapy (eg, prednisone or hydrocortisone) and corticosteroid use to manage AEs are permitted. Autoimmune disorders requiring chronic systemic steroid therapy or any other form of immunosuppressive therapy. Patient may be included if the treatment is discontinued more than months prior to the first dose of AMG at a low likelihood of relapse AND if there is agreement by both the investigator and the Amgen Medical Monitor. Has received systemic steroid therapy or any other form of immunosuppressive therapy within days prior to registration for protocol therapy Diagnosis of immunodeficiency or receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of study therapy; the use of physiologic doses of corticosteroids may be approved after consultation with the study principal investigator (PI) Immunocompromised patients and patients with known immunodeficiency; or receiving systemic steroid therapy or any other immunosuppressive therapy =< days prior to registration; NOTE: inhaled steroids and low-dose corticosteroids are allowed Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within weeks of the first protocol treatment; the use of low-dose steroids for management of chronic conditions is allowed Has a diagnosis of immunodeficiency or is receiving systemic immunosuppressive steroid therapy or any other form of systemic immunosuppressive therapy within days prior to the first dose of trial treatment; exception: physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency is not considered systemic immunosuppressive steroid therapy Receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of trial treatment; patients who have received acute, low-dose, systemic immunosuppressant medications (e.g., limited low-dose dexamethasone for nausea, multiple doses for contrast allergy) may be enrolled in the study and would not require a day washout Is receiving systemic steroid therapy < days before the first dose of study drug or receiving any other form of immunosuppressive medication. Receiving TNF pathway inhibitors, PI kinase inhibitors, systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of study drug Has a diagnosis of immunodeficiency OR is receiving a systemic steroid therapy exceeding physiologic corticosteroid dose or any other form of immunosuppressive therapy within days prior to randomization, except in the case of central nervous system (CNS) metastases. Subject is on any systemic steroid therapy, within one week before the planned date for first dose of study treatment. Subject is on any other form of immunosuppressive medication Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within seven days prior to the first dose of trial treatment. The use of physiologic doses of corticosteroids may be approved after consultation with the Sponsor. Receiving TNF pathway inhibitors, PI kinase inhibitors, systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of study drug Has a diagnosis of immunodeficiency or is receiving any systemic steroid therapy or any other form of immunosuppressive therapy within days prior to Day of trial treatment. The use of physiologic doses of corticosteroids may be approved after consultation with the Sponsor. Receiving systemic steroid therapy <= days prior to first dose of study drug or receiving any other form of immunosuppressive medication Receiving systemic steroid therapy within days prior to the first dose of study treatment or receiving any other form of immunosuppressive medication Within days prior to the planned start of study treatment:\r\n* Is receiving systemic steroid therapy or any other form of immunosuppressive therapy Patients receiving systemic treatment with systemic steroid therapy or any other immunosuppressive medication at any dose level that would interfere with the action of the study drugs in the opinion of the investigator Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of trial treatment, exceptions include topical, intralesional, intraarticular and inhaled steroids; a pulse steroid dose prior to and after imaging to prevent contrast allergy in patients with known allergy to contrast is allowed Diagnosis of immunosuppression or receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of study medication Systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of study medication Diagnosis of immunodeficiency or receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of study medication (physiologic doses of corticosteroids may be approved after consultation with the Sponsor) Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of trial treatment; the use of physiologic doses of corticosteroids may be approved after consultation with the sponsor Any condition requiring active steroid or other immunosuppressive therapy Subject is receiving systemic steroid therapy or any other form of immunosuppressive therapy within weeks prior to first dose of study treatment. Has a diagnosis of immunodeficiency or receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of study treatment. The use of physiologic doses of corticosteroids may be approved after consultation with the Sponsor. Systemic steroids, any other form of immunosuppressive therapy or radiation therapy within days prior to registration. Diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy (including immune modulators or systemic corticosteroids) within days prior to study enrollment. Systemic steroid or other immunosuppressive therapy within weeks of starting the study Systemic steroid (except inhaled steroids) or other immunosuppressive therapy administered for more than days within weeks of enrollment Diagnosis of immunosuppression or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of trial treatment; the use of physiologic doses of corticosteroids may be approved after consultation with the sponsor Subjects on chronic steroid therapy, other immunosuppressive therapy Receiving systemic steroid therapy or any form of immunosuppressive therapy within days prior to first injection of [F]F-AraG\r\n* Topical and inhaled corticosteroids are allowed Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of trial treatment; subjects requiring systemic steroids are excluded from the trial; the use of physiologic doses of corticosteroids may be approved after discussion with the sponsor Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of trial treatment; subjects requiring systemic steroids are excluded from the trial; the use of physiologic doses of corticosteroids may be approved after discussion with the sponsor Diagnosis of immunosuppression or receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to enrollment . The use of physiologic doses of corticosteroids may be approved after consultation with the sponsor. Has a diagnosis of immunosuppression or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within days prior to the first dose of study drug.