ABSTRACT The atomic resolution structures of the human immunodeficiency virus type 1 (HIV-1) Gag lattice have revealed critical molecular contacts that stabilize the HIV-1 immature particle structure and have informed HIV- 1 proteolytic cleavages and Gag lattice disassembly. In order to gain a fundamental understanding of retrovirus assembly and maturation, atomic resolution maps of immature particles for the Orthoretrovirinae are required. Here we propose a strategy, i.e., cryo-electron tomography (cryo-ET) guided single particle reconstruction (SPR), to achieve atomic resolution reconstruction maps of retrovirus immature particles. We will use human immunodeficiency virus type 2 (HIV-2) as the basis for implementation of this image processing strategy. We will then apply the method to the study of other retrovirus immature particle structures, e.g., human T-cell leukemia virus type 1 (HTLV-1), and conduct comparative studies about the conservation of key molecular interactions in HIV-1, HIV-2 and HTLV-1 Gag lattice structures. We will also apply this approach for the study of membrane anchored HIV-1 envelope protein structure. This proposed hybrid image processing method takes advantage of the strengths of both cryo-EM imaging methods (i.e. cryo-ET and SPR) and overcomes the computation challenges that each method bears when processing images of retrovirus immature particles.