The following group has reported the results of a study of cross-antibodies between the new coronavirus (SARS-CoV-2) and coronavirus (HCoVs) that contribute to the seasonal cold.
https://science.sciencemag.org/content/early/2020/11/05/science.abe1107
The HCoVs antibodies seem to have the effect of suppressing SARS-CoV-2 infection with the cross-reactivity for people who have never infected with the new coronavirus.
This cross-antibody is not targeting RBD of SARS-CoV-2 as the epitope, but common amino acid sequences in the S2 region seem to be the ones as shown below.
In addition, since the retention rate of the cross-antibody is high in young people, it may be related to the phenomenon that young people are less likely to develop the severe illness of COVID-19.