The present invention relates to, among others, an in vitro method of modifying a cell graft containing immune cells comprising the steps of incubating a cell graft containing immune cells with an anti CD4 antibody wherein said incubating is carried out for from 1 minute to 7 days, b) removing unbound antibody from said graft; as well as to corresponding modified grafts and uses. The invention further relates to the modification of antibodies reactive to the CD4 human leukocyte antigen to provide anti-CD4 antibodies that have a reduced number of potential T-cell epitopes but retain the ability to bind to CD4, such as to an anti human CD4-antibody comprising a heavy chain immunoglobulin variable domain (VH) and a light chain immunoglobulin variable domain (VL), wherein at least one T cell epitope located outside the CDRs of said immunoglobulin variable domains is removed from said immunoglobulin variable domains. Preferably, the specificity and mode of action of the anti-CD4 antibodies are not affected by the modification(s).