Received a live vaccine within 30 days of the first dose of study medication Administration of a live vaccine within 30 days prior to first dose of study drug Received a live vaccine within 30 days prior to first dose of study drug Has received a live vaccine within 30 days prior to the first dose of study therapy Has received a live-virus vaccine within 30 days prior to first dose of study medication. Has received a live vaccine within 30 days prior to the first dose of study therapy Have received a live vaccine within 30 days before the first dose of study treatment. Has received a live vaccine within 30 days prior to first dose of study drug. Received a vaccine within 7 days of first dose Received a live vaccine within 30 days of the first dose of treatment. Has received a live attenuated vaccine within 28 days before the first dose of study drug Has received a live vaccine within 30 days prior to the first dose of study drug Has received a live vaccine within 30 days prior to the first dose of study treatment. Patients who have received live, attenuated vaccine within 28 days prior to the first dose of PD-1 inhibitor. Has received a live vaccine within 30 days prior to the first dose of study drug Has received a live vaccine within 30 days prior to first dose Patients who have received a live vaccine within 30 days prior to the first dose of pembrolizumab Has received a live attenuated vaccine within 28 days before the first dose of study drug Subjects must not have received a live vaccine within 30 days prior to the first dose of study medication Have received a live vaccine within 30 days before the first dose of study treatment. Has received a live vaccine within 30 days prior to the first dose of study drug Received a live vaccine within 30 days prior to first dose of study drug Patient has received a live vaccine within 4 weeks prior to the first dose of treatment Have received any live vaccine within 14 days prior to first study drug administration. Received a live attenuated vaccine within 28 days of first study dose, unable to take oral medications Has received a live vaccine within 30 days prior to the first dose of study treatment Received a live vaccine within 30 days prior to the first dose of study treatment. Patient has received a live vaccine within 30 days prior to first dose Received a live vaccine within 1 week prior to the first dose of study treatment Has received a live vaccine within 30 days of the first dose of study therapy Has received a live vaccine within 30 days prior to first dose of study drug. Received a live vaccine within 30 days prior to the first dose of study medication Live vaccine use within 30 days of first dose of study medication. Has taken any prohibited medications that are listed in the protocol within 14 days of the first dose of study treatment. Subject has received or will receive a live vaccine within 30 days before the first administration of study treatment Has received a live vaccine within 30 days prior to first dose. Received or will receive a live vaccine within 30 days prior to first dose of study drug Received a live vaccine within 30 days prior to first dose of study drug Received a live vaccine within 30 days of the first dose of study medication Treatment with live vaccine within 30 days prior to the first dose of study medication are not eligible Has received a live vaccine within 30 days prior to the first dose of study drug Has received a live vaccine within 30 days prior to the first dose of study drug Has received a live vaccine within 30 days prior to the first dose of study treatment Has received a live vaccine within 30 days prior to the first dose of study treatment Has received a live vaccine within 30 days of the first dose of study treatment. Has received a live vaccine within 30 days prior to first dose of study therapy Have received a live vaccine within 30 days before the first dose of study treatment Received live, attenuated vaccine within 28 days prior to the first dose of mogamulizumab; Has received a live vaccine within 30 days prior to first dose Has received a live vaccine within 30 days prior to the first dose of study therapy Has received a live vaccine within 30 days prior to the first dose of study treatment Has received a live vaccine within 30 days prior to the first dose of study treatment. Has received a live-virus vaccine within 30 days prior to the first dose of study treatment Received a live viral vaccine within 6 months prior to the first dose of study drug. Has received a live vaccine within 30 days prior to first dose of study drug. Received a live vaccine =< 30 days prior to registration Vaccinations with a live vaccine within 28 days prior to start of treatment or need for live vaccine at any time during study treatment. Has received a live vaccine ? 30 days prior to study registration Has received a live vaccine within 30 days prior to the initiation of lymphodepletion. Has received a live vaccine within 28 days prior to registration Received live vaccine within 28 days prior to enrollment Live vaccine ? 4 weeks prior to enrollment Received any live vaccine within the last 30 days Patients who have received a live vaccine within 30 days prior initiation of the systemic regimen Received a live vaccine within 4 weeks prior to the start of study drug Patients who have received a live vaccine within 30 days prior initiation of the systemic regimen Has received a live vaccine within 30 days of first study procedure (apheresis) Received a live vaccine within 30 days prior to start of study treatment Received a live vaccine =< 30 days prior to registration Received live vaccine within 28 days prior to enrollment Received a live vaccine =< 30 days prior to registration Has received a live vaccine within 30 days prior to registration Received a live vaccine within 30 days of first protocol treatment Patients who have received a live attenuated vaccine =< 30 days prior to registration are not eligible Received live vaccine =< 30 days prior to registration History of receiving a live vaccine 30 days prior to study treatment. Received live vaccine within 28 days prior to enrollment Live vaccine within 30 days prior to treatment initiation. Patients who have received a live vaccine within 30 days prior to the radiation therapy Has received a live vaccine within 30 days prior to the first protocol treatment Received any live vaccine =< 30 days prior to registration Has received a live vaccine within 30 days prior to transplant admission Has received a live virus vaccine within 30 days of allocation. Has received a live virus vaccine within 30 days of randomization. Received live vaccine within 28 days prior to enrollment Subject has received a live virus vaccine within the previous 8 weeks. Patients planning for a live vaccine Live vaccine ? 6 weeks prior to start of conditioning regimen Has received a live vaccine within 30 days prior to trial registration. Has received a live vaccine within 30 days prior to the radiation therapy Live vaccine within 30 days prior to registration. Patient who have received a live vaccine within 30 days prior to cycle 1 day 1 Participant has received a live vaccine within 2 weeks (less than 14 days) prior to C1D1 Subject has received a live vaccine within 4 weeks prior to C1D1 Any patient receiving a live vaccine must allow a 4-week interval before starting treatment on this study Participant has received a live vaccine within 4 weeks prior to screening Received live vaccine within 28 days prior to enrollment Received a live vaccine within 30 days prior to day 1 Live vaccine ? 4 weeks prior to enrollment Received live vaccine within 28 days prior to enrollment. Has received a live vaccine within 30 days prior to randomization. Received live vaccine within 28 days prior to enrollment. Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment SAFETY RUN-IN: Has received a live vaccine within 30 days prior to the first dose of trial treatment RANDOMIZED PHASE II CLINICAL TRIAL: Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial drug. Has received a live vaccine within 30 days prior to the first dose of trial treatment Live vaccine within 4 weeks of the first dose of pembrolizumab and while on trial is prohibited Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Have received a live vaccine within 30 days prior to the first dose of trial treatment. Received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Subject has received a live vaccine within 30 days prior to the first dose of trial treatment Have received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment. Is known to have received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment The participant has received a live vaccine within 30 days prior to the first dose of trial treatment. Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Patients who have received a live vaccine within 30 days prior to the first dose of trial treatment. Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Has received a live vaccine within 30 days prior to the first dose of trial treatment Have received a live-virus vaccine within 30 days prior to planned treatment start. Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 28 days of planned start of study therapy Has received a live vaccine within 28 days of planned start of study therapy Patients who have received a live vaccine within 30 days of the planned start of study therapy Must not have received a live vaccine within 30 days of planned start of the study therapy Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of study therapy Received live vaccine within 30 days of planned start of study medication Received a live vaccine within 30 days of planned start of study medication Has received a live vaccine within 28 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of trial therapy. Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of study therapy Received a live virus vaccine within 30 days of planned start of therapy Has received a live vaccine within 30 days of planned start of study therapy. Received a live virus vaccine within 30 days of planned start of study treatment Has received a live vaccine within 30 days of planned start of study therapy. Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 30 days of planned start of study therapy Received a live vaccine =< 30 days of planned start of study therapy Received a live vaccine within 30 days of planned start of study medication Has received a live vaccine within 30 days of planned start of study drug (Cycle 1, Day 1). Has received a live vaccine within 30 days of planned start of study therapy. Live vaccine within 30 days of planned start of study drug Received a live virus vaccine within 30 days of planned study start Has received a live virus vaccine within 30 days of planned start of trial treatment Has received a live vaccine within 30 days of planned start of study drug (Cycle 1, Day 1) Has received a live vaccine within 30 days of the planned first dose of the study Receipt of a live vaccine within 30 days of planned start of study therapy. Received a live vaccine within 30 days of planned start of study medication Live vaccine within 30 days of planned start of study therapy Received a live vaccine within 30 days of planned start of study medication Received a live virus vaccine within 30 days of planned start of study treatment Received a live virus vaccine within 30 days of planned start of trial treatment Received live vaccine within 30 days of planned start of study therapy Live vaccine within 30 days of planned start of study therapy Has received live vaccine within 30 days of the planned start of study therapy Received a live vaccine within 30 days of planned start of study treatment Has received a live vaccine within 30 days of planned start of study therapy. Has received a live vaccine within 30 days prior to the planned first dose of study therapy. Patient who received a live vaccine within 30 days of planned start of study therapy Patient who received a live vaccine within 30 days of planned start of study therapy Has received a live vaccine within 28 days of planned start of study therapy Received a live vaccine within 30 days of planned PD-1 start date. Receipt of a live vaccine within 30 days of planned start of study drug. Receipt of a live vaccine within 30 days of planned start of study therapy Has received a live-virus vaccination within 30 days of planned treatment start. Seasonal flu vaccines that do not contain live virus are permitted. Received a live-virus vaccination within 30 days of planned treatment start. Has received a live vaccine within 30 days of the planned start of study therapy. Seasonal flu vaccines that do not contain live virus are permitted. Live-virus vaccination -4 weeks NOTE: Seasonal flu vaccines that do not contain live virus are not an exclusion. Received live-virus vaccination within 30 days (seasonal flu vaccine allowed if non-live virus) Has received a live-virus vaccine within 30 days of planned start of study drug. Seasonal flu vaccines that do not contain live virus are permitted. Has received a live-virus vaccination within 28 days of planned treatment start. Seasonal flu vaccines that do not contain live virus are permitted. Live-virus vaccination within 30 days of the first dose of mRNA-4157 or pembrolizumab. Seasonal flu vaccines that do not contain live virus are permitted Has received a live-virus vaccination within 30 days of planned treatment start. Has received a live-virus vaccination within 30 days of planned treatment start Has received a live-virus vaccination within 30 days of planned treatment start. Seasonal flu vaccines that do not contain live virus are permitted Has received a live-virus vaccination within 30 days of planned start of study therapy. Seasonal flu vaccines that do not contain live virus are permitted. Has received a live-virus vaccination within 30 days of planned treatment start. Note: Seasonal flu vaccines that do not contain live virus are permitted. Has received or will receive a live vaccine within 30 days prior to the first administration of study medication; seasonal flu vaccines that do not contain live virus are permitted Has received a live-virus vaccination within 30 days of planned treatment start. Seasonal flu vaccines that do not contain live virus are permitted. Has received a live-virus vaccination within 30 days of planned treatment start. Previous treatment with live vaccine within 30 days of planned start of study drugs (seasonal flu vaccines that do not contain a live virus are permitted). Has received a live-virus vaccination within 30 days prior to start of study drug treatment. a. Seasonal flu and other inactivated vaccines that do not contain live virus are permitted. Receipt of live vaccination within 28 days before randomization; seasonal flu vaccines that do not contain live virus are permitted Has received a live-virus vaccination within 30 days of planned treatment start. Note: Seasonal flu vaccines that do not contain live virus are permitted. Received a live-virus vaccination within 30 days of planned start of study medication. Has received a live vaccine within 30 days of the planned start of study therapy. Seasonal flu vaccines that do not contain live virus are permitted. Have received a live vaccine within 30 days prior to enrollment. Seasonal flu vaccines that do not contain live virus are permitted. Has received a live-virus vaccination within 30 days of planned treatment start Participant has received a live-virus vaccination within 30 days of planned treatment start. Seasonal flu vaccines that do not contain live virus are permitted. Has received a live-virus vaccination within 30 days of planned treatment start. Seasonal flu vaccines that do not contain live virus are permitted Has received a live-virus vaccination within 30 days of planned start of study therapy. Seasonal flu vaccines that do not contain live virus are permitted. Patients must not have received any live vaccine within 30 days prior to registration; seasonal flu vaccines that do not contain live virus are permitted