The present investigations focus on the development of an antibody-based (IgG) endogenous drug delivery system for the systemic delivery of CpG oligodeoxynucleotides (CpG-ODNs) in the immunotherapeutic treatment of solid tumors. Four fundamental observations support this research: (i) current CpG-ODN immunotherapeutic regimens require frequent intra/peritumoral(local) injections, restricting their application to external solid tumors only, (ii) endogenous IgG and monomeric immune complexes (1:1 stoichiometry) have a long circulation half-life, slow clearance, low volume of tissue distribution, and passively extravasate into the tumor periphery via the Enhanced Permeability and Retention (EPR) effect, (iii) the cellular targets for CpG-ODN are peritumoral dendritic cells and macrophages, which highly express Fc= receptors. These receptors endocytose IgG and monomeric immune complexes via their Fc portion, and (iv) the molecular receptor for CpG-ODN, TLR 9, is located inside the endosome. To this end, the binding affinity of model ODNs to antidinitrophenyl (DNP) IgG was optimized through the strategic derivatization of DNP epitopes (Chapter II). The premise behind this study was to obtain the highest affinity iv complex between DNP-ODNs and anti-DNP IgG, as to prevent ODN systemic dissociation. Accordingly, the chosen bivalent design yielded a 66-fold enhancement in binding affinity and was used to derivatize CpG-ODNs for in vivo studies. Pharmacokinetic (PK) and biodistribution analysis of bivalent, monovalent, and underivatized immunotherapeutic CpG oligodeoxynucleotides in a DNP-immunized, syngeneic tumor-bearing mouse model ensued (Chapter III). The prolonged half-life, reduced volume of distribution, slowed systemic clearance, and enhanced tumor accumulation observed during this investigation for both monovalent and bivalent DNPCpG- ODNs warranted further pharmacodynamic studies (Chapter IV). In this case, however, only the monovalent conjugate was tested for its ability to inhibit tumor growth in the same animal model. Its physiological effect was also assessed through gross physiological observation and histological analysis of lymphoid organs (liver and spleen) and solid tumors. As expected, the systemic disposition profile of DNP-CpG-ODN observed during PK studies correlated to an enhanced therapeutic efficacy as this formulation inhibited the growth of solid tumors and elicited necrosis of tumoral tissue. All together, these findings attest to the validity of this drug delivery approach for the targeted systemic immunotherapeutic treatment of solid tumors.